c++: Improve diagnostics for constexpr cast from void*

This patch improves the errors given when casting from void* in C++26 to
include the expected type if the types of the pointed-to objects were
not similar. It also ensures (for all standard modes) that void* casts
are checked even for DECL_ARTIFICIAL declarations, such as
lifetime-extended temporaries, and is only ignored for cases where we
know it's OK (e.g. source_location::current) or have no other choice
(heap-allocated data).

gcc/cp/ChangeLog:

	* constexpr.cc (is_std_source_location_current): New.
	(cxx_eval_constant_expression): Only ignore cast from void* for
	specific cases and improve other diagnostics.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-cast4.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Marek Polacek  <polacek@redhat.com>
Reviewed-by: Jason Merrill <jason@redhat.com>

0 files changed, 0 insertions, 0 deletions