[Linux] Enable build IDs.

We should use build IDs on Linux so that we can identify the built
artefacts, and also so that we can match them up with debug
information should we choose to separate it.

rdar://130582882

Author: al45tair

CMakeLists.txt

@@ -23,6 +23,14 @@ endif()
 
 include(SwiftSupport)
 include(GNUInstallDirs)
+include(CheckLinkerFlag)
+
+if(CMAKE_SYSTEM_NAME STREQUAL Linux
+    OR CMAKE_SYSTEM_NAME STREQUAL FreeBSD
+    OR CMAKE_SYSTEM_NAME STREQUAL OpenBSD)
+  enable_language(C)
+  check_linker_flag(C "LINKER:--build-id=sha1" LINKER_SUPPORTS_BUILD_ID)
+endif()
 
 add_library(XCTest
   Sources/XCTest/Private/WallClockTimeMetric.swift
@@ -79,6 +87,10 @@ set_target_properties(XCTest PROPERTIES
   Swift_MODULE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/swift
   INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_BINARY_DIR}/swift)
 
+if(LINKER_SUPPORTS_BUILD_ID)
+  target_link_options(XCTest PRIVATE "LINKER:--build-id=sha1")
+endif()
+
 
 if(ENABLE_TESTING)
   enable_testing()