c++: Output less irrelevant info for function template decl [PR100716]

c++: Output less irrelevant info for function template decl [PR100716]

Ensure dump_template_decl for function templates never prints template
parameters after the function name (it did with -fno-pretty-templates)
and skip output of irrelevant & confusing "[with T = T]" in
dump_substitution.

gcc/cp/ChangeLog:

	PR c++/100716
	* error.c (dump_template_bindings): Include code to print
	"[with" and ']', conditional on whether anything is printed at
	all. This is tied to whether a semicolon is needed to separate
	multiple template parameters. If the template argument repeats
	the template parameter (T = T), then skip the parameter.
	(dump_substitution): Moved code to print "[with" and ']' to
	dump_template_bindings.
	(dump_function_decl): Partial revert of PR50828, which masked
	TFF_TEMPLATE_NAME for all of dump_function_decl. Now
	TFF_TEMPLATE_NAME is masked for the scope of the function and
	only carries through to dump_function_name.
	(dump_function_name): Avoid calling dump_template_parms if
	TFF_TEMPLATE_NAME is set.

gcc/testsuite/ChangeLog:

	PR c++/100716
	* g++.dg/diagnostic/pr100716.C: New test.
	* g++.dg/diagnostic/pr100716-1.C: Same test with
	-fno-pretty-templates.