cmd/go: fix check for -Wp,-U in cgo CFLAGS

There should be no space after comma.

Change-Id: I6a5c85a386d9d1611b71d5b15a31a00c24c316b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/210120
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -52,7 +52,7 @@ var validCompilerFlags = []*lazyregexp.Regexp{
 	re(`-W([^@,]+)`), // -Wall but not -Wa,-foo.
 	re(`-Wa,-mbig-obj`),
 	re(`-Wp,-D([A-Za-z_].*)`),
-	re(`-Wp, -U([A-Za-z_]*)`),
+	re(`-Wp,-U([A-Za-z_]*)`),
 	re(`-ansi`),
 	re(`-f(no-)?asynchronous-unwind-tables`),
 	re(`-f(no-)?blocks`),

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

@@ -22,6 +22,8 @@ var goodCompilerFlags = [][]string{
 	{"-Osmall"},
 	{"-W"},
 	{"-Wall"},
+	{"-Wp,-Dfoo=bar"},
+	{"-Wp,-Ufoo"},
 	{"-fobjc-arc"},
 	{"-fno-objc-arc"},
 	{"-fomit-frame-pointer"},