testsuite: Fix up lra effective target

Given the recent discussions on IRC started with Andrew P. mentioning that
an asm goto outputs test should have { target lra } and the lra effective
target in GCC 11/12 only returning 0 for PA and in 13/14 for PA/AVR, while
we clearly have 14 other targets which don't support LRA and a couple of
further ones which have an -mlra/-mno-lra switch (whatever default they
have), seems to me the effective target is quite broken.

The following patch rewrites it, such that it has a fast path for heavily
used targets which are for years known to use only LRA (just an
optimization) plus determines whether it is a LRA target or reload target
by scanning the -fdump-rtl-reload-details dump on an empty function,
LRA has quite a few always emitted messages in that case while reload has
none of those.

Tested on x86_64-linux and cross to s390x-linux, for the latter with both
make check-gcc RUNTESTFLAGS='--target_board=unix/-mno-lra dg.exp=pr107385.c'
where the test is now UNSUPPORTED and
make check-gcc RUNTESTFLAGS='--target_board=unix/-mlra dg.exp=pr107385.c'
where it fails because I don't have libc around.

There is one special case, NVPTX, which is a TARGET_NO_REGISTER_ALLOCATION
target.  I think claiming for it that it is a lra target is strange (even
though it effectively returns true for targetm.lra_p ()), unsure if it
supports asm goto with outputs or not, if it does and we want to test it,
perhaps we should introduce asm_goto_outputs effective target and use
lra || nvptx-*-* for that?

2024-02-17  Jakub Jelinek  <jakub@redhat.com>

	* lib/target-supports.exp (check_effective_target_lra): Rewrite
	to list some heavily used always LRA targets and otherwise check the
	-fdump-rtl-reload-details dump for messages specific to LRA.