Fix AX_GCC_FUNC_ATTRIBUTE failure

[remicollet]

AX_GCC_FUNC_ATTRIBUTE([target]) may fail breaking various optimization (ex: base64_encode/base64_decode)

In config.log

configure:17050: checking for __attribute__((target))
configure:17072: cc -o conftest -Wall -Werror=format-security -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Werror=incompatible-pointer-types -fvisibility=hidden  -D_GNU_SOURCE  conftest.c -lm  >&5
conftest.c:146:32: warning: 'bar' declared 'static' but never defined [-Wunused-function]
  146 |                     static int bar( void ) __attribute__((target("sse2")));
      |                                ^~~
configure:17072: $? = 0
configure:17087: result: no

Dropping the static keyword allow the test to work

Notice, this file is outdated, see http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_gcc_func_attribute.m4 (serial 9 => 13) but "target" is not part of this upstream file, and only ifunc and target are used.

[petk]

I was checking if this should be added in the upstream archive, but the issue is that this target addition is very specific and would require additional argument (that "sse2" string). #11712 and this is also in need of rechecking #9586

I think this macro can be forked and bundled but we update it with the upstream recent changes.

[remicollet]

Thanks for the quick review

Merged in 8.2+ as 09a3681

[athos-ribeiro]

Hi, @remicollet, I just saw this one landed. Thanks for fixing that.

FWIW, we are still carrying #9586 in Debian/Ubuntu since any new warnings introduced would disable those optimizations in future builds.