race.bash, race.bat: build a race enabled cmd/cgo before trying to use it

Fixes #5537.

To avoid `go install -v race std` replacing cmd/cgo with a race enabled version and another package trying to build a cgo enabled package, always build cmd/cgo race enabled before doing the rest of the build.

R=remyoudompheng, rsc, dvyukov, minux.ma
CC=golang-dev
https://golang.org/cl/14071044

src/race.bash

@@ -35,6 +35,8 @@ if [ ! -f make.bash ]; then
 	exit 1
 fi
 . ./make.bash --no-banner
+# golang.org/issue/5537 - we must build a race enabled cmd/cgo before trying to use it.
+go install -race cmd/cgo
 go install -race std
 go test -race -short std
 go test -race -run=nothingplease -bench=.* -benchtime=.1s -cpu=4 std

src/race.bat

@@ -29,6 +29,9 @@ goto fail
 :continue
 call make.bat --no-banner --no-local
 if %GOBUILDFAIL%==1 goto end
+:: golang.org/issue/5537 - we must build a race enabled cmd/cgo before trying to use it.
+echo # go install -race cmd/cgo
+go install -race cmd/cgo
 echo # go install -race std
 go install -race std
 if errorlevel 1 goto fail