Merging r353402:

------------------------------------------------------------------------
r353402 | mstorsjo | 2019-02-07 13:46:49 +0100 (Thu, 07 Feb 2019) | 7 lines

[clang-cl] support /Oy- on aarch64

MSVC supports /Oy- on aarch64, so clang-cl should too.

Patch by Nathan Froyd!

Differential Revision: https://reviews.llvm.org/D57838
------------------------------------------------------------------------

llvm-svn: 353829