cmd/dist: remove race binaries when rebuilding everything

Fixes #13214.

Change-Id: Id8fbb252b8beadb0b41f839dcd85d6165dea86a3
Reviewed-on: https://go-review.googlesource.com/16845Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/dist/build.go

@@ -909,6 +909,8 @@ func clean() {
 		// Remove installed packages and tools.
 		xremoveall(pathf("%s/pkg/%s_%s", goroot, gohostos, gohostarch))
 		xremoveall(pathf("%s/pkg/%s_%s", goroot, goos, goarch))
+		xremoveall(pathf("%s/pkg/%s_%s_race", goroot, gohostos, gohostarch))
+		xremoveall(pathf("%s/pkg/%s_%s_race", goroot, goos, goarch))
 		xremoveall(tooldir)
 
 		// Remove cached version info.