[flang] Add --gcc-toolchain and --gcc-install-dir options to flang. (llvm#87360)

The `--gcc-toolchain` and `--gcc-install-dir` option were previously only visible to the Clang driver, but not Flang. These determine which assembler, linker, and libraries to use, e.g. for cross-compiling, and therefore are relevant for Flang as well.

Tests are implemented using a mock GCC installation in `basic_cross_linux_tree` copied over from Clang's tests. The Clang driver already contains tests with `--driver-mode=flang` but `flang-new` is an entirely different executable (containing the `-fc1` stage) that should be tested as well. While not all files in `basic_cross_linux_tree` are strictly needed for testing those two driver flags, they will be necessarily needed for future added flags such as `--rtlib`.
 
Also remove the entry `*.o` in flang's `.gitignore` since `crt*.o` files are needed in the GCC mock installation.

Fixes llvm#86729

Author: Meinersbur

clang/include/clang/Driver/Options.td

@@ -802,9 +802,11 @@ def B : JoinedOrSeparate<["-"], "B">, MetaVarName<"<prefix>">,
     HelpText<"Search $prefix$file for executables, libraries, and data files. "
     "If $prefix is a directory, search $prefix/$file">;
 def gcc_install_dir_EQ : Joined<["--"], "gcc-install-dir=">,
+  Visibility<[ClangOption, FlangOption]>,
   HelpText<"Use GCC installation in the specified directory. The directory ends with path components like 'lib{,32,64}/gcc{,-cross}/$triple/$version'. "
   "Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation">;
 def gcc_toolchain : Joined<["--"], "gcc-toolchain=">, Flags<[NoXarchOption]>,
+  Visibility<[ClangOption, FlangOption]>,
   HelpText<"Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. "
   "Clang will use the GCC installation with the largest version">;
 def gcc_triple_EQ : Joined<["--"], "gcc-triple=">,

flang/.gitignore

@@ -5,7 +5,6 @@ build
 root
 tags
 TAGS
-*.o
 .nfs*
 *.sw?
 *~

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/i386-unknown-linux-gnu-as

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/i386-unknown-linux-gnu-ld

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/i386-unknown-linux-gnu-ld.bfd

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/i386-unknown-linux-gnu-ld.gold

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/x86_64-unknown-linux-gnu-as

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/x86_64-unknown-linux-gnu-ld

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/x86_64-unknown-linux-gnu-ld.bfd

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/bin/x86_64-unknown-linux-gnu-ld.gold

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/i386-unknown-linux-gnu/bin/as

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/i386-unknown-linux-gnu/bin/ld

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/i386-unknown-linux-gnu/bin/ld.bfd

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/i386-unknown-linux-gnu/bin/ld.gold

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/i386-unknown-linux-gnu/lib/.keep

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0/crtbegin.o

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/crtbegin.o

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/crtbeginT.o

@@ -0,0 +1 @@
+#!/bin/true

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/crtfastmath.o

@@ -104,6 +104,9 @@
 ! CHECK-NEXT: -fversion-loops-for-stride
 ! CHECK-NEXT:                         Create unit-strided versions of loops
 ! CHECK-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
+! CHECK-NEXT: --gcc-install-dir=<value>
+! CHECK-NEXT:                         Use GCC installation in the specified directory. The directory ends with path components like 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation
+! CHECK-NEXT: --gcc-toolchain=<value> Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Clang will use the GCC installation with the largest version
 ! CHECK-NEXT: -gline-directives-only  Emit debug line info directives only
 ! CHECK-NEXT: -gline-tables-only      Emit debug line number tables only
 ! CHECK-NEXT: -gpulibc                Link the LLVM C Library for GPUs

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/x32/crtbegin.o

@@ -92,6 +92,9 @@
 ! HELP-NEXT: -fversion-loops-for-stride
 ! HELP-NEXT:                         Create unit-strided versions of loops
 ! HELP-NEXT: -fxor-operator          Enable .XOR. as a synonym of .NEQV.
+! HELP-NEXT: --gcc-install-dir=<value>
+! HELP-NEXT:                         Use GCC installation in the specified directory. The directory ends with path components like 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation
+! HELP-NEXT: --gcc-toolchain=<value> Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. Clang will use the GCC installation with the largest version
 ! HELP-NEXT: -gline-directives-only  Emit debug line info directives only
 ! HELP-NEXT: -gline-tables-only      Emit debug line number tables only
 ! HELP-NEXT: -gpulibc                Link the LLVM C Library for GPUs

flang/test/Driver/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/x32/crtbeginT.o

@@ -0,0 +1,21 @@
+!! Test that --gcc-toolchain and --gcc-install-dir options are working as expected.
+!! It does not test cross-compiling (--sysroot), so crtbegin.o, libgcc/compiler-rt, libc, libFortranRuntime, etc. are not supposed to be affected.
+!! PREFIX is captured twice because the driver escapes backslashes (occuring in Windows paths) in the -### output, but not on the "Selected GCC installation:" line.
+
+! RUN: %flang 2>&1 -### -v -o %t %s -no-integrated-as -fuse-ld=ld --target=i386-unknown-linux-gnu --gcc-install-dir=%S/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0 | FileCheck %s --check-prefix=CHECK-I386
+! RUN: %flang 2>&1 -### -v -o %t %s -no-integrated-as -fuse-ld=ld --target=i386-unknown-linux-gnu --gcc-toolchain=%S/Inputs/basic_cross_linux_tree/usr                                         | FileCheck %s --check-prefix=CHECK-I386
+! CHECK-I386:      Selected GCC installation: [[PREFIX:[^"]+]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0
+! CHECK-I386:      "-fc1" "-triple" "i386-unknown-linux-gnu" 
+! CHECK-I386:      "[[PREFIX:[^"]+]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0/../../../../i386-unknown-linux-gnu/bin{{/|\\\\}}as"
+! CHECK-I386:      "[[PREFIX]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0/../../../../i386-unknown-linux-gnu/bin{{/|\\\\}}ld" {{.*}} "-m" "elf_i386"
+! CHECK-I386-SAME: "-L[[PREFIX]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0" 
+! CHECK-I386-SAME: "-L[[PREFIX]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/i386-unknown-linux-gnu/10.2.0/../../../../i386-unknown-linux-gnu/lib"
+
+! RUN: %flang 2>&1 -### -v -o %t %s -no-integrated-as -fuse-ld=ld --target=x86_64-unknown-linux-gnu --gcc-install-dir=%S/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0 | FileCheck %s --check-prefix=CHECK-X86-64
+! RUN: %flang 2>&1 -### -v -o %t %s -no-integrated-as -fuse-ld=ld --target=x86_64-unknown-linux-gnu --gcc-toolchain=%S/Inputs/basic_cross_linux_tree/usr                                           | FileCheck %s --check-prefix=CHECK-X86-64
+! CHECK-X86-64:      Selected GCC installation: [[PREFIX:[^"]+]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0
+! CHECK-X86-64:      "-fc1" "-triple" "x86_64-unknown-linux-gnu"
+! CHECK-X86-64:      "[[PREFIX:[^"]+]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/../../../../x86_64-unknown-linux-gnu/bin{{/|\\\\}}as" "--64"
+! CHECK-X86-64:      "[[PREFIX]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/../../../../x86_64-unknown-linux-gnu/bin{{/|\\\\}}ld" {{.*}} "-m" "elf_x86_64"
+! CHECK-X86-64-SAME: "-L[[PREFIX]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0" 
+! CHECK-X86-64-SAME: "-L[[PREFIX]]/Inputs/basic_cross_linux_tree/usr/lib/gcc/x86_64-unknown-linux-gnu/10.2.0/../../../../x86_64-unknown-linux-gnu/lib"