cmd/go: reject buildmode=pie when -race is enabled

Fixes #20038

Change-Id: Id692790ea406892bbe29090d461356bac28b6150
Reviewed-on: https://go-review.googlesource.com/41333Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/internal/work/build.go

@@ -313,6 +313,9 @@ func BuildModeInit() {
 		pkgsFilter = pkgsMain
 		ldBuildmode = "exe"
 	case "pie":
+		if cfg.BuildRace {
+			base.Fatalf("-buildmode=pie not supported when -race is enabled")
+		}
 		if gccgo {
 			base.Fatalf("-buildmode=pie not supported by gccgo")
 		} else {