cmd/go: preserve CC for TestScript child processes

    
    Reviewed-on: https://go-review.googlesource.com/c/158838

From-SVN: r269240

gcc/go/gofrontend/MERGE

-558fcb7bf2a6b78bdba87f20a8a4a95d27125d74
+9c1859b8e97242b0e697a3aaa39a4da5e6172e74
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/cmd/go/script_test.go

@@ -83,13 +83,12 @@ type backgroundCmd struct {
 }
 
 var extraEnvKeys = []string{
-	"SYSTEMROOT",      // must be preserved on Windows to find DLLs; golang.org/issue/25210
-	"LD_LIBRARY_PATH", // must be preserved on Unix systems to find shared libraries
-
-	// For gccgo testing.
-	"GO_TESTING_GOTOOLS",
-	"GCCGO",
-	"GCCGOTOOLDIR",
+	"SYSTEMROOT",         // must be preserved on Windows to find DLLs; golang.org/issue/25210
+	"LD_LIBRARY_PATH",    // must be preserved on Unix systems to find shared libraries
+	"CC",                 // don't lose user settings when invoking cgo
+	"GO_TESTING_GOTOOLS", // for gccgo testing
+	"GCCGO",              // for gccgo testing
+	"GCCGOTOOLDIR",       // for gccgo testing
 }
 
 // setup sets up the test execution temporary directory and environment.