[release-branch.go1.4] make.bash: set CGO_ENABLED=0

cgo is not supported with 1.4.

In addition to (perhaps instead of) documenting it,
just enforce it in make.*.

Updates Homebrew/homebrew-core#18465

Change-Id: Iefb1860890d9ec525597b6d730e2189110818598
Reviewed-on: https://go-review.googlesource.com/124076
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

src/make.bash

@@ -106,6 +106,13 @@ if [ "$(uname -s)" == "GNU/kFreeBSD" ]; then
         export CGO_ENABLED=0
 fi
 
+# cgo is not generally supported on 1.4.
+# Disable unless explicitly requested.
+# See also https://github.com/Homebrew/homebrew-core/issues/18465.
+if [ "$CGO_ENABLED" == "" ]; then
+	export CGO_ENABLED=0
+fi
+
 # Clean old generated file that will cause problems in the build.
 rm -f ./runtime/runtime_defs.go
 

src/make.bat

@@ -37,6 +37,12 @@ setlocal
 
 set GOBUILDFAIL=0
 
+:: cgo is not generally supported on 1.4.
+:: Disable unless explicitly requested.
+if not x%CGO_ENABLED%==x goto cgodone
+set CGO_ENABLED=0
+:cgodone
+
 if exist make.bat goto ok
 echo Must run make.bat from Go src directory.
 goto fail 

src/make.rc

@@ -45,6 +45,11 @@ rm -f ./runtime/runtime_defs.go
 # Determine the host compiler toolchain.
 eval `{grep '^(CC|LD|O)=' /$objtype/mkfile}
 
+# cgo is not generally supported on 1.4.
+# Disable unless explicitly requested.
+if(~ $CGO_ENABLED '')
+	CGO_ENABLED = 0
+
 echo '# Building C bootstrap tool.'
 echo cmd/dist
 GOROOT = `{cd .. && pwd}