bitint: Fix tree node sharing bug [PR114209]

bitint: Fix tree node sharing bug [PR114209]

We ICE on the following testcase due to invalid tree sharing.
The second hunk fixes that, the first one is from me looking around at
other spots which might need end up with invalid tree sharing too.

2024-03-04  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/114209
	* gimple-lower-bitint.cc (bitint_large_huge::limb_access): Call
	unshare_expr when creating a MEM_REF from MEM_REF.
	(bitint_large_huge::lower_stmt): Call unshare_expr.

	* gcc.dg/bitint-97.c: New test.