c++: lambda in template default argument [PR103186]

c++: lambda in template default argument [PR103186]

The problem with this testcase was that since my patch for PR97900 we
weren't preserving DECL_UID identity for parameters of instantiations of
templated functions, so using those parameters as the keys for the
defarg_inst map broke.  I think this was always fragile given the
possibility of redeclarations, so instead of reverting that change let's
switch to keying off the function.

Memory use compiling stdc++.h is not noticeably different.

	PR c++/103186

gcc/cp/ChangeLog:

	* pt.cc (defarg_inst): Use tree_vec_map_cache_hasher.
	(defarg_insts_for): New.
	(tsubst_default_argument): Adjust.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/lambda/lambda-defarg10.C: New test.