[libc] Capture floating point encoding and arrange it sequentially in memory

Redefined FPBits.h and LongDoubleBitsX86 so its implementation works for the Windows
and Linux platform while maintaining a packed memory alignment of the precision floating
point numbers. For its size in memory to be the same as the data type of the float point number.
This change was necessary because the previous attribute((packed)) specification in the struct was not working
for Windows like it was for Linux and consequently static_asserts in the FPBits.h file were failing.

Reviewed By: aeubanks, sivachandra

Differential Revision: https://reviews.llvm.org/D105561