[PATCH v5] Add TEST_CC and TEST_CXX support

[Sam James]

"H.J. Lu" <hjl.tools@gmail.com> writes:

> Changes in v5:
>
> 1. Fix a typo.
> 2. Update sysdeps/x86_64/configure.ac for GCC 6
>
> ---
> Support testing glibc build with a different C compiler or a different
> C++ compiler with
>
> $ ../glibc-VERSION/configure TEST_CC="gcc-6.4.1" TEST_CXX="g++-6.4.1"
>
> 1. Also check compiler options with TEST_CC and TEST_CXX.
> 2. Add check and xcheck targets to Makefile.in and override build compiler
> options with ones from TEST_CC and TEST_CXX.
>
> Tested on Fedora 41/x86-64:
>
> 1. Building with GCC 14.2.1 and testing with GCC 6.4.1 and GCC 11.2.1.
> 2. Building with GCC 15 and testing with GCC 6.4.1.
>
> Support for GCC versions older than GCC 6.2 may need to change the test
> sources.  Other targets may need to update configure.ac under sysdeps and
> modify Makefile.in to override target build compiler options.

Please fix sysdeps/x86_64/configure.ac's libc_cv_test_x86_have_amx_tile
check which fails to restore CC.