cmd/go: accept "-F dir" in compiler flags

Fixes #51008

Change-Id: I5e47c7be59d4aae1d5059d99231422212cffa23a
Reviewed-on: https://go-review.googlesource.com/c/go/+/383217
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

Author: ianlancetaylor

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

@@ -131,6 +131,7 @@ var validCompilerFlagsWithNextArg = []string{
 	"-D",
 	"-U",
 	"-I",
+	"-F",
 	"-framework",
 	"-include",
 	"-isysroot",

src/cmd/go/internal/work/security_test.go

@@ -15,6 +15,7 @@ var goodCompilerFlags = [][]string{
 	{"-Ufoo"},
 	{"-Ufoo1"},
 	{"-F/Qt"},
+	{"-F", "/Qt"},
 	{"-I/"},
 	{"-I/etc/passwd"},
 	{"-I."},