[libc] Add on float properties for precision floating point numbers in FloatProperties.h

Defined constant that express the number of bits for exponent in single and double precision. Added bit masks values and other properties for quad precision floating point numbers that specifically targets architectures defined in PlatfromDefs.h. The exponentWidth values were added to be used in LongDoubleBitsX86.h where the implementation to set the exponent component uses this and the bitWidth value. The need occurred because of the 80-bit quad precision implementation.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D105153