[X86][MS] Change the alignment of f80 to 16 bytes on Windows 32bits to match with ICC

MSVC currently doesn't support 80 bits long double. ICC supports it when
the option `/Qlong-double` is specified. Changing the alignment of f80
to 16 bytes so that we can be compatible with ICC's option.

Reviewed By: rnk, craig.topper

Differential Revision: https://reviews.llvm.org/D115942