Add support for gcc as git submodule of another repository.

	contrib/
	* gcc_update: Check for .git as a file.

From-SVN: r259819

contrib/ChangeLog

+2018-05-01  Jim Wilson  <jimw@sifive.com>
+
+	* gcc_update: Check for .git as a file.
+
 2018-03-21  Christophe Lyon  <christophe.lyon@linaro.org>
 
 	* test_summary: Match possible single quotes in configure path.

contrib/gcc_update

@@ -286,7 +286,7 @@ p
 esac
 
 # Check for known version control systems.
-if [ -d .git ]; then
+if [ -d .git ] || [ -f .git ]; then
     GCC_GIT=${GCC_GIT-${GIT-git}}
     vcs_type="git"
 elif [ -d .hg ]; then