misc/cgo: fix wrong quote character

Single quotes to not expand variables inside of them.

Change-Id: I4a0622c0aebfc1c3f9d299f93f7a8253893b5858
Reviewed-on: https://go-review.googlesource.com/13661Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/testcshared/test.bash

@@ -10,7 +10,7 @@ set -e
 
 if [ ! -f src/libgo/libgo.go ]; then
 	cwd=$(pwd)
-	echo 'misc/cgo/testcshared/test.bash is running in $cwd' 1>&2
+	echo "misc/cgo/testcshared/test.bash is running in $cwd" 1>&2
 	exit 1
 fi