ninja depot_tools script: Call ninja-mac on mac.

Review URL: http://codereview.chromium.org/9214014

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@117754 0039d316-1c4b-4281-b951-d872f2087c98

ninja

@@ -1,3 +1,13 @@
-#!/bin/sh
+#!/bin/bash
+
+OS="$(uname -s)"
+
+if [ "${OS}" = "Linux" ]; then
+  exec ninja-linux64 "$@"
+elif [ "${OS}" = "Darwin" ]; then
+  exec ninja-mac "$@"
+else
+  echo "Unsupported OS ${OS}"
+  exit 1
+fi
 
-exec ninja-linux64 "$@"