Use linker flag --fix-cortex-a53-843419 on Android ARM64 compilation.

Summary:
This is only forced on if there is no non-Cortex-A53 CPU specified as
well. Android's platform and NDK builds need to assume that the code can
be run on Cortex-A53 devices, so we always enable the fix unless we know
specifically that the code is only running on a different kind of CPU.

Reviewers: cfe-commits

Subscribers: aemerson, rengolin, tberghammer, pirama, danalbert

Differential Revision: https://reviews.llvm.org/D25761

llvm-svn: 285127