[COFF, ARM64] Align global symbol by size for ARM64 MSVC ABI

According to alignment section in below ARM64 ABI document, MSVC could increase
alignment of global data based on its total size. Clang doesn't do this. Compile
the same symbol into different alignments by Clang and MSVC could cause link
error because some instruction encodings, like 64-bit LDR/STR with immediate,
require the target to be 8 bytes aligned, and linker could choose code stream
with such LDR/STR instruction from MSVC and 4 bytes aligned data from Clang into
final image, which actually cannot be linked together
(see https://bugs.llvm.org/show_bug.cgi?id=41506 for more details).

https://docs.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions?view=vs-2019#alignment

Differential Revision: https://reviews.llvm.org/D61225

llvm-svn: 359744