d: Fix struct literals that have non-deterministic hash values (PR96153)

d: Fix struct literals that have non-deterministic hash values (PR96153)

Adds code generation for generating a temporary for, and pre-filling
struct and array literals with zeroes before assigning, so that
alignment holes don't cause objects to produce a non-deterministic hash
value.  A new field has been added to the expression visitor to track
whether the result is being generated for another literal, so that
memset() is only called once on the top-level literal expression, and
not for nesting struct or arrays.

gcc/d/ChangeLog:

	PR d/96153
	* d-tree.h (build_expr): Add literalp argument.
	* expr.cc (ExprVisitor): Add literalp_ field.
	(ExprVisitor::ExprVisitor): Initialize literalp_.
	(ExprVisitor::visit (AssignExp *)): Call memset() on blits where RHS
	is a struct literal.  Elide assignment if initializer is all zeroes.
	(ExprVisitor::visit (CastExp *)): Forward literalp_ to generation of
	subexpression.
	(ExprVisitor::visit (AddrExp *)): Likewise.
	(ExprVisitor::visit (ArrayLiteralExp *)): Use memset() to pre-fill
	object with zeroes.  Set literalp in subexpressions.
	(ExprVisitor::visit (StructLiteralExp *)): Likewise.
	(ExprVisitor::visit (TupleExp *)): Set literalp in subexpressions.
	(ExprVisitor::visit (VectorExp *)): Likewise.
	(ExprVisitor::visit (VectorArrayExp *)): Likewise.
	(build_expr): Forward literal_p to ExprVisitor.

gcc/testsuite/ChangeLog:

	PR d/96153
	* gdc.dg/pr96153.d: New test.