mesa: don't call git if it's not git repository

Reviewed-by: Dan Nicholson <dbn.lists@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

bin/extract_git_sha1

@@ -3,6 +3,10 @@ if [ ! -f src/mesa/main/git_sha1.h ]; then
 	touch src/mesa/main/git_sha1.h
 fi
 
+if [ ! -d .git ]; then
+	exit
+fi
+
 if which git > /dev/null; then
     # Extract the 7-digit "short" SHA1 for the current HEAD, convert
     # it to a string, and wrap it in a #define.  This is used in