cmd/go: permit additional cflags when compiling

In CL 475375 the Go command started to generate the "preferlinkext"
token file for "strange/dangerous" compiler flags. This serves as a hint
to the Go linker whether to call the external linker or not.

Permit compiler flag used by the hermetic_cc_toolchain bzlmod.

As a side effect, it also allows these flags to appear
in #cgo directives in source code. We don't know of any cases
where that is actually useful, but it appears to be harmless
and simplifies the implementation of the internal linking change.

Fixes #72842

Change-Id: Ic6de29b535a4e2c0720f383567ea6b3c7ca4f541
Reviewed-on: https://go-review.googlesource.com/c/go/+/657575
Auto-Submit: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>

Author: Holger Hans Peter Freyther

src/cmd/go/internal/work/security.go

@@ -90,6 +90,7 @@ var validCompilerFlags = []*lazyregexp.Regexp{
 	re(`-f(no-)?use-linker-plugin`), // safe if -B is not used; we don't permit -B
 	re(`-f(no-)?visibility-inlines-hidden`),
 	re(`-fsanitize=(.+)`),
+	re(`-fsanitize-undefined-strip-path-components=(-)?[0-9]+`),
 	re(`-ftemplate-depth-(.+)`),
 	re(`-ftls-model=(global-dynamic|local-dynamic|initial-exec|local-exec)`),
 	re(`-fvisibility=(.+)`),

src/cmd/go/testdata/script/cgo_suspect_flag_force_external.txt

@@ -56,6 +56,14 @@ env CGO_CFLAGS=-fprofile-instr-generate
 go build -x -n -o dummy.exe ./usesInternalCgo
 stderr preferlinkext
 
+# Trimming file information for the UndefinedBehaviorSanitizer is permitted for internal linking.
+env CGO_CFLAGS=-fsanitize-undefined-strip-path-components=-1
+go build -x -n -o dummy.exe ./usesInternalCgo
+! stderr preferlinkext
+env CGO_CFLAGS=-fsanitize-undefined-strip-path-components=2
+go build -x -n -o dummy.exe ./usesInternalCgo
+! stderr preferlinkext
+
 # The -fdebug-prefix-map=path is permitted for internal linking.
 env CGO_CFLAGS=-fdebug-prefix-map=/some/sandbox/execroot/workspace=/tmp/new
 go build -x -n -o dummy.exe ./usesInternalCgo