[X86] Add CPU string output to...

[X86] Add CPU string output to getIntelProcessorTypeAndSubtype/getAMDProcessorTypeAndSubtype in Host.cpp

Rather than converting type/subtype into strings, just directly
select the string as part of family/model decoding. This avoids
the need for creating fake Type/SubTypes for CPUs not supported
by compiler-rtl. I've left the Type/SubType in place where it matches
compiler-rt so that the code can be diffed, but the Type/SubType
is no longer used by Host.cpp.

compiler-rt was already updated to select strings that aren't used
so the code will look similar.