decl alignment not respected

decl alignment not respected

This patch cures a problem with ICF of read-only variables at the
intersection of -fsection-anchors, -ftree-loop-vectorize, and targets
with alignment restrictions.

What happens with the testcase is:
- "c" is referenced in a constructor, thus make_decl_rtl for "c",
- make_decl_rtl puts "c" in an anchor block (-fsection-anchors),
- anchor block contents can't move, so "c" alignment can't change by
  ipa_increase_alignment (-ftree-loop-vectorize),
- however "a" alignment can be increased,
- ICF aliases "a" to "c".
So we have a decl for "a" saying it is aligned to 128 bits, using mem
for "c" which is only 16 bit aligned.

	PR ipa/69990
gcc/
	* ipa-icf.c (sem_variable::merge): Do not merge an alias with
	larger alignment.
gcc/testsuite/
	gcc.dg/pr69990.c: New.

From-SVN: r233906