Broken ./configure checks for __cpuid() and __cpuidex()

Hi all,

While looking at patch 0001 posted by Lukas at [1], the following bit
stood out as an independent fix:
+++ b/configure
 unsigned int exx[4] = {0, 0, 0, 0};
-  __get_cpuidex(exx[0], 7, 0);
+  __cpuidex(exx, 7, 0);

The patch posted is incorrect because it does not touch configure.ac
and an autoreconf -i or equivalent is missing, but it does not change
the fact that this looks like a valid issue to me.

While looking at the surroundings, I have noticed a second check
that's incorrect in ./configure.ac, with __cpuid().  I may be missing
something, of course, but these two typos have been introduced by
3dc2d62d0486, back in 2015.  meson is doing these checks correctly.  I
have not been able to test that on cirrus, it seems to run into
problems this morning.  I don't know much about these instructions,
but it seems like __get_cpuid_count() and __get_cpuid() are much more
populate than the two others, so the impact may be lighter than I
suspect for builds using ./configure.

Equally, I think that one comment in meson.build is just a consequence
of these two typos.

The attached warrants a backpatch to me, thoughts?

Thanks,

[1]: https://www.postgresql.org/message-id/CAP53Pky-BN0Ui+A9no3TsU=GoMTFpxYSWYtp_LVaDH=y69BxNg@mail.gmail.com
--
Michael