internal/syscall: add cgo_import_dynamic for Fchmodat on AIX and Solaris

For #67002

Change-Id: I1709fd51ba52c074501420943d311c785a49d851
Reviewed-on: https://go-review.googlesource.com/c/go/+/649015
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Damien Neil <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: neild

src/internal/syscall/unix/at_aix.go

@@ -4,6 +4,7 @@
 
 package unix
 
+//go:cgo_import_dynamic libc_fchmodat fchmodat "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_fstatat fstatat "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_openat openat "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_unlinkat unlinkat "libc.a/shr_64.o"

src/internal/syscall/unix/at_solaris.go

@@ -13,6 +13,7 @@ func syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err
 func rawSyscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
 //go:cgo_import_dynamic libc_faccessat faccessat "libc.so"
+//go:cgo_import_dynamic libc_fchmodat fchmodat "libc.so"
 //go:cgo_import_dynamic libc_fstatat fstatat "libc.so"
 //go:cgo_import_dynamic libc_openat openat "libc.so"
 //go:cgo_import_dynamic libc_unlinkat unlinkat "libc.so"