Fix breakpad on mips and x86_64 for the NDK r10c update.

This change introduces the necessary glue typedefs to deal with the
mismatch introduced by the latest Android NDK (w.r.t. desktop Linux):
- [x86_64] Rename fpregs mxcr_mask -> .mxcsr_mask
- [mips] uc_mcontext.fpregs.fp_r.fp_dregs -> uc_mcontext.fpreg
- [mips] restore the forked user.h

Submitting this on behalf of fdegans@chromium.org

TBR=mark@chromium.org

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1397 4c0a9323-5329-0410-9bdc-e9ce6186880e