Declare MVT::SimpleValueType as an int8_t sized enum. This removes 400 bytes...

Declare MVT::SimpleValueType as an int8_t sized enum. This removes 400 bytes from TargetLoweringBase and probably other places.

This required changing several places to print VT enums as strings instead of raw ints since the proper method to use to print became ambiguous. This is probably an improvement anyway.

This also appears to save ~8K from an x86 self host build of llc.

llvm-svn: 266562