d: Ensure casting from bool results in either 0 or 1 (PR96435)

d: Ensure casting from bool results in either 0 or 1 (PR96435)

If casting from bool, the result is either 0 or 1, any other value
violates @safe code, so enforce that it is never invalid.

	PR d/96435

gcc/d/ChangeLog:

	* d-convert.cc (convert_for_rvalue): New function.
	* d-tree.h (convert_for_rvalue): Declare.
	* expr.cc (ExprVisitor::visit (CastExp *)): Use convert_for_rvalue.
	(build_return_dtor): Likewise.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr96435.d: New test.

(cherry picked from commit 5c9b7408dc578cb2ae142a5c1b724c183497bdb2)