Fix failure building LLVM with location wrapper nodes (PR c++/83799)

Fix failure building LLVM with location wrapper nodes (PR c++/83799)

PR c++/83799 reports a failure building LLVM due to a bogus
"no matching function for call to" error at a callsite like this:
  TLI->getTypeLegalizationCost(DL);
where "DL" is from:
  using TargetTransformInfoImplBase::DL;

The root cause is that type_dependent_expression_p on a USING_DECL
should return true when processing a template, but after r256448 the
the argument at the callsite is a location wrapper around the USING_DECL,
and type_dependent_expression_p erroneously returns false for it, as
it is comparing tree codes, and failing a match, then looking at types.

This prevents cp_parser_postfix_expression from using the
"build_min_nt_call_vec" path for handling the call, instead erroneously
handling it via build_new_method_call (which fails for this case).

This patch fixes the problem by stripping any location wrappers before
the various tree code tests in type_dependent_expression_p.   It fixes
the reduced test case, and the full BasicTargetTransformInfo.ii; after
this patch, the assembly generated for that latter case is identical to
that generated before r256448.

gcc/cp/ChangeLog:
	PR c++/83799
	* pt.c (type_dependent_expression_p): Strip any location wrapper
	before testing tree codes.
	(selftest::test_type_dependent_expression_p): New function.
	(selftest::cp_pt_c_tests): Call it.

gcc/testsuite/ChangeLog:
	PR c++/83799
	* g++.dg/wrappers/pr83799.C: New test case.

From-SVN: r256796