Android.rules: build x86 tests with -mstackrealign

All android builds systems have switched to -mstackrealign for building
x86 binaries, so follow their cue with our mini build system.

This presently breaks just one test (TestReturnValue), and this is due
to a compiler bug, which has already been fixed in clang, but it hasn't
made it yet into the official NDK compiler. While I'm touching that
test, I also remove an android-specific XFAIL, which is not relevant
anymore.

llvm-svn: 306683