d: Fix core.volatile.volatileLoad discarded if result is unused

d: Fix core.volatile.volatileLoad discarded if result is unused

The first pass of code generation in the D front-end splits up all
compound expressions and discards expressions that have no side effects.
This included calls to the `volatileLoad' intrinsic if its result was
not used, causing such calls to be eliminated from the program.

We already set TREE_THIS_VOLATILE on the expression, however the
tree documentation says if this bit is set in an expression, so is
TREE_SIDE_EFFECTS.  So set TREE_SIDE_EFFECTS on the expression too.
This prevents any early discarding from occuring.

	PR d/110516

gcc/d/ChangeLog:

	* intrinsics.cc (expand_volatile_load): Set TREE_SIDE_EFFECTS on the
	expanded expression.
	(expand_volatile_store): Likewise.

gcc/testsuite/ChangeLog:

	* gdc.dg/torture/pr110516a.d: New test.
	* gdc.dg/torture/pr110516b.d: New test.