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

This reverts commit c2d85eb.

Reason for revert: change was incorrect. ignores setting of CGO_ENABLED in some cases

Change-Id: I8e6e68dd600be5306a247a3314f4b57175f1aa56
Reviewed-on: https://go-review.googlesource.com/c/go/+/705495
Auto-Submit: Michael Matloob <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Reviewed-by: Ian Alexander <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: matloob

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

@@ -145,8 +145,7 @@ func defaultContext() build.Context {
 	if buildcfg.DefaultCGO_ENABLED == "1" {
 		defaultCgoEnabled = true
 	} else if buildcfg.DefaultCGO_ENABLED == "0" {
-	}
-	if runtime.GOARCH == ctxt.GOARCH && runtime.GOOS == ctxt.GOOS {
+	} else 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