c++: Fix ICE with CONSTRUCTOR flags verification [PR93559]

c++: Fix ICE with CONSTRUCTOR flags verification [PR93559]

Since reshape_init_array_1 can now reuse a single constructor for
an array of non-aggregate type, we might run into a scenario where
we reuse a constructor with TREE_SIDE_EFFECTS.  This broke this test
because we have something like { { expr } } and we try to reshape it,
so we recurse on the inner CONSTRUCTOR, reuse an existing CONSTRUCTOR
with TREE_SIDE_EFFECTS, and then ICE on the discrepancy because the
outermost CONSTRUCTOR doesn't have TREE_SIDE_EFFECTS.  In this case
EXPR was a call to an operator function so TREE_SIDE_EFFECTS should
be set.  Naturally one would want to fix this by calling
recompute_constructor_flags in an appropriate place so that the flags
on the CONSTRUCTORs match.  The appropriate place would be at the end
of reshape_init, but this breaks initlist109.C: there we are dealing
with { { TARGET_EXPR <{}> } } where the outermost { } is TREE_CONSTANT
but the inner { } is not, so recompute_constructor_flags would clear
the constant flag in the outermost { }.  Seems resonable but it upsets
check_initializer which then complains about "non-constant in-class
initialization invalid for static member".  TARGET_EXPRs are always
created with TREE_SIDE_EFFECTS on, but that is mutually exclusive
with TREE_CONSTANT.  So we're in a bind.

Fixed by not reusing a CONSTRUCTOR that has TREE_SIDE_EFFECTS; in the
grand scheme of things it isn't measurable: it only affects ~3 tests
in the testsuite.

	PR c++/93559 - ICE with CONSTRUCTOR flags verification.
	* decl.c (reshape_init_array_1): Don't reuse a CONSTRUCTOR with
	TREE_SIDE_EFFECTS.

	* g++.dg/cpp0x/initlist119.C: New test.
	* g++.dg/cpp0x/initlist120.C: New test.