[AsmParser] Add source location to all errors related to .cfi directives

I was trying to add .cfi_ annotations to assembly code in the FreeBSD
kernel and changed a macro that then resulted in incorrectly nested
directives. However, clang's diagnostics said the error was happening at
<unknown>:0. This addresses one of the TODOs added in D51695.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D89787