Patch improves next things:
* Fixes assert/crash in getOpDesc when giving it a invalid expression op code.
* DWARFExpression::print() called DWARFExpression::Operation::getEndOffset() which
returned and used uninitialized field EndOffset. Patch fixes that.
* Teaches verifier to verify DW_AT_location and error out on broken expressions.
Differential revision: https://reviews.llvm.org/D39294
llvm-svn: 316756