c++: consteval propagation and templates [PR115986]

c++: consteval propagation and templates [PR115986]

Here the call to e() makes us decide to check d() for escalation at EOF, but
while checking it we try to fold_immediate 0_c, and get confused by the
template trees.  Let's not mess with escalation for function templates.

	PR c++/115986

gcc/cp/ChangeLog:

	* cp-gimplify.cc (remember_escalating_expr): Skip function
	templates.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/consteval-prop21.C: New test.