cmd/dist: remove -Werror from CFLAGS

Fixes #12345.

Change-Id: I43d91e3f33171c333803036b29c3238c6aff3c60
Reviewed-on: https://go-review.googlesource.com/13962Reviewed-by: Andrew Gerrand <adg@golang.org>

src/cmd/dist/build.c

@@ -482,7 +482,6 @@ static char *proto_gccargs[] = {
 	"-Wno-switch",
 	"-Wno-comment",
 	"-Wno-missing-field-initializers",
-	"-Werror",
 	"-fno-common",
 	"-ggdb",
 	"-pipe",