CGDebugInfo CreatedLimitedType: Drop file/line for RecordType with invalid location

For Clang synthesized `__va_list_tag` (`CreateX86_64ABIBuiltinVaListDecl`),
its DW_AT_decl_file/DW_AT_decl_line are arbitrarily set from `CurLoc`.

In a stage 2 `-DCMAKE_BUILD_TYPE=Debug` clang build, I observe that
in driver.cpp, DW_AT_decl_file/DW_AT_decl_line may be set to an `#include` line
(the transitively included file uses va_arg (`__builtin_va_arg`)).
This seems arbitrary. Drop that.

Reviewed By: #debug-info, dblaikie

Differential Revision: https://reviews.llvm.org/D94735