cmd/go: fix buildvcs when using older git versions

Git versions before v2.10.0 do not support --no-show-signature.
Using "-c" allows Git to ignore the configuration option if it does not
exist.

Fixes #51253

Change-Id: I2b1adaca0eb18ae31f2e1119e354ce515b00cfc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/388194
Trust: Dmitri Shuralyov <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: mpx

src/cmd/go/internal/vcs/vcs.go

@@ -312,7 +312,7 @@ func gitStatus(vcsGit *Cmd, rootDir string) (Status, error) {
 	// uncommitted files and skip tagging revision / committime.
 	var rev string
 	var commitTime time.Time
-	out, err = vcsGit.runOutputVerboseOnly(rootDir, "show -s --no-show-signature --format=%H:%ct")
+	out, err = vcsGit.runOutputVerboseOnly(rootDir, "-c log.showsignature=false show -s --format=%H:%ct")
 	if err != nil && !uncommitted {
 		return Status{}, err
 	} else if err == nil {

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

@@ -111,7 +111,7 @@ rm $GOBIN/d$GOEXE
 go list -x ./...
 stdout -count=3 '^example.com'
 stderr -count=1 '^git status'
-stderr -count=1 '^git show'
+stderr -count=1 '^git -c log.showsignature=false show'
 
 -- $WORK/fakebin/git --
 #!/bin/sh