i386: Fix rtl checking ICE in ix86_elim_entry_set_got [PR112837]

i386: Fix rtl checking ICE in ix86_elim_entry_set_got [PR112837]

The following testcase ICEs with RTL checking, because it sets if
XINT (SET_SRC (set), 1) is UNSPEC_SET_GOT without checking if SET_SRC (set)
is actually an UNSPEC, so any time we see any other insn with PARALLEL
and a SET in it which is not an UNSPEC we ICE during RTL checking or
access there some other union member as if it was an rt_int.
The rest is just small cleanup.

2023-12-04  Jakub Jelinek  <jakub@redhat.com>

	PR target/112837
	* config/i386/i386.cc (ix86_elim_entry_set_got): Before checking
	for UNSPEC_SET_GOT check that SET_SRC is UNSPEC.  Use SET_SRC and
	SET_DEST macros instead of XEXP, rename vec variable to set.

	* gcc.dg/pr112837.c: New test.