c++: passing partially inst tmpl as ttp [PR110566]

c++: passing partially inst tmpl as ttp [PR110566]

Since the template arguments 'pargs' we pass to coerce_template_parms from
coerce_template_template_parms are always a full set, we need to make sure
we always pass the parameters of the most general template because if the
template is partially instantiated then the levels won't match up.  In the
testcase below during said call to coerce_template_parms the parameters are
{X, Y}, both level 1 rather than 2, and the arguments are {{int}, {N, M}},
which results in a crash during auto deduction for parameters' types.

	PR c++/110566
	PR c++/108179

gcc/cp/ChangeLog:

	* pt.cc (coerce_template_template_parms): Simplify by using
	DECL_INNERMOST_TEMPLATE_PARMS and removing redundant asserts.
	Always pass the parameters of the most general template to
	coerce_template_parms.

gcc/testsuite/ChangeLog:

	* g++.dg/template/ttp38.C: New test.