Disable GNU extensions in bspatch code.

Bspatch uses fopencookie(3) and some other GNU extensions not
implemented on mac and some targets. This patch fixes the build by
disabling the code using those features, that will be re-enabled on a
follow up CL.

Change-Id: Ibc7975b3ab6b4afa7c7ac1ee445173973a2a570a
Test: `mmma external/bsdiff` on the target and on mac.