runtime/cgo: add -fno-stack-protector to CFLAGS

Some compilers default to having -fstack-protector on, which breaks
when using internal linking because the linker doesn't know how to
find the support functions.

Fixes golang#52919
Fixes golang#54313

Change-Id: I6f51d5e906503f61fc768ad8e30c163bad135087
Reviewed-on: https://go-review.googlesource.com/c/go/+/421935
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

src/runtime/cgo/cgo.go

@@ -23,7 +23,9 @@ package cgo
 #cgo solaris LDFLAGS: -lxnet
 #cgo solaris LDFLAGS: -lsocket
 
-#cgo CFLAGS: -Wall -Werror
+// We use -fno-stack-protector because internal linking won't find
+// the support functions. See issues #52919 and #54313.
+#cgo CFLAGS: -Wall -Werror -fno-stack-protector
 
 #cgo solaris CPPFLAGS: -D_POSIX_PTHREAD_SEMANTICS