[PR88534] accept VAR_DECL in class literal template parms

[PR88534] accept VAR_DECL in class literal template parms

P0732R2 / C++ 2a introduce class literals as template parameters.  The
front-end uses VAR_DECLs constructed from such literals to bind the
template PARM_DECLs, but dwarf2out.c used to reject such VAR_DECLs.

Taking DECL_INITIAL from such VAR_DECLs enables the generation of
DW_AT_const_value for them, at least when the class literal can
actually be represented as such.

for  gcc/ChangeLog

	PR c++/88534
	PR c++/88537
	* dwarf2out.c (generic_parameter_die): Follow DECL_INITIAL of
	VAR_DECL args.

for  gcc/testsuite/ChangeLog

	PR c++/88534
	PR c++/88537
	* g++.dg/cpp2a/pr88534.C: New.
	* g++.dg/cpp2a/pr88537.C: New.

From-SVN: r269709