cmd/go: whitelist -v as a compiler and linker flag

It's harmless, and can be useful to see what's happening under the hood.

Fixes #24593.

Change-Id: Iacff378471e86c33aa048161cd65c504709fb339
Reviewed-on: https://go-review.googlesource.com/115075
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -94,6 +94,7 @@ var validCompilerFlags = []*regexp.Regexp{
 	re(`-?-stdlib=([^@\-].*)`),
 	re(`-w`),
 	re(`-x([^@\-].*)`),
+	re(`-v`),
 }
 
 var validCompilerFlagsWithNextArg = []string{
@@ -127,6 +128,7 @@ var validLinkerFlags = []*regexp.Regexp{
 	re(`-shared`),
 	re(`-?-static([-a-z0-9+]*)`),
 	re(`-?-stdlib=([^@\-].*)`),
+	re(`-v`),
 
 	// Note that any wildcards in -Wl need to exclude comma,
 	// since -Wl splits its argument at commas and passes

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

@@ -57,6 +57,7 @@ var goodCompilerFlags = [][]string{
 	{"-I", "世界"},
 	{"-framework", "Chocolate"},
 	{"-x", "c"},
+	{"-v"},
 }
 
 var badCompilerFlags = [][]string{
@@ -132,6 +133,7 @@ var goodLinkerFlags = [][]string{
 	{"-l", "世界"},
 	{"-L", "framework"},
 	{"-framework", "Chocolate"},
+	{"-v"},
 	{"-Wl,-framework", "-Wl,Chocolate"},
 	{"-Wl,-framework,Chocolate"},
 	{"-Wl,-unresolved-symbols=ignore-all"},