Make sure sys.platform isn't required

Update darwin handler so it will fall back to the standard *nix method
if Python isn't installed as a framework.


[SVN r37211]

tools/build

@@ -1 +1 @@
-Subproject commit 444fa3c2549d8eae4ef4fa2e3c2d4d448a2196f3
+Subproject commit 549a94389e2276c91cd95ca257d093d27f99eb37