c++: Revert EXPR_LOCATION change to build_aggr_init_expr [PR96997]

c++: Revert EXPR_LOCATION change to build_aggr_init_expr [PR96997]

My change in r10-7718 to make build_aggr_init_expr set EXPR_LOCATION
(mimicking build_target_expr) causes the debuginfo regression PR96997.
Given that this change is mostly independent of the rest of the commit,
and that the only fallout of reverting it is a less accurate error
message location in a testcase introduced in the same commit, it seems
the best way forward is to just revert this part of the commit.

gcc/cp/ChangeLog:

	PR debug/96997
	PR c++/94034
	* tree.c (build_aggr_init_expr): Revert r10-7718 change.

gcc/testsuite/ChangeLog:

	PR debug/96997
	PR c++/94034
	* g++.dg/cpp1y/constexpr-nsdmi7b.C:  Adjust expected location of
	"call to non-'constexpr' function" error message.