cmd/go: disable cgo by default if CC unset and DefaultCC doesn't exist

CL 621995 disrupted the behavior
introduced by CL 450739, now restore it.

Fixes #75340

Change-Id: Icd1a0eb970876995f9446e0547ceb9e78990f6ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/703555
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Reviewed-by: Ian Alexander <[email protected]>
Reviewed-by: Sean Liao <[email protected]>

Author: qiulaidongfeng

src/cmd/go/internal/cfg/cfg.go

@@ -145,7 +145,8 @@ func defaultContext() build.Context {
 	if buildcfg.DefaultCGO_ENABLED == "1" {
 		defaultCgoEnabled = true
 	} else if buildcfg.DefaultCGO_ENABLED == "0" {
-	} else if runtime.GOARCH == ctxt.GOARCH && runtime.GOOS == ctxt.GOOS {
+	}
+	if runtime.GOARCH == ctxt.GOARCH && runtime.GOOS == ctxt.GOOS {
 		defaultCgoEnabled = platform.CgoSupported(ctxt.GOOS, ctxt.GOARCH)
 		// Use built-in default cgo setting for GOOS/GOARCH.
 		// Note that ctxt.GOOS/GOARCH are derived from the preference list