[DebugInfo] Error out when enabling -fdebug-types-section on non-ELF target.

Currently, support for debug_types is only present for ELF and trying to
pass -fdebug-types-section for other targets results in a crash in the
backend. Until this is fixed, we should emit a diagnostic in the front
end when the option is passed for non-linux targets.

Differential revision: https://reviews.llvm.org/D49594

llvm-svn: 337717