configure.ac: using $CC to check compiler names may result in erroneous judgements

[kanavin]

configure.ac contains multiple checks of this kind:

case $CC in

When paths contain "clang"/"gcc"/"icc", they might be part of $CC
for example because of the "--sysroot" parameter. That could cause
judgement error about clang/gcc/icc compilers. e.g.

when "icc" is containded in working path, below errors are reported when compiling python3:

x86_64-wrs-linux-gcc: error: strict: No such file or directory
x86_64-wrs-linux-gcc: error: unrecognized command line option '-fp-model'

Linked PRs

• gh-96398: Improve accuracy of compiler checks in configure.ac #117815
• gh-96398: Detect emcc and mpicc in compiler names in configure #117819
• gh-96398: Detect GCC compatible compilers in configure #117825
• gh-96398: Purge Emscripten code from configure.ac #117836
• gh-96398: Fix mpicc check in configure.ac #117857

[tiran]

We are aware that the checks are problematic have already plans to replace $CC checks with $ac_cv_cc_name. It's a new variable that I introduced a short while ago.

[tiran]

CC @erlend-aasland @mdboom

[erlend-aasland]

cc. @corona10

[erlend-aasland]

A quick summary:

#110034 points out that we've got various attempts to detect the compiler version in configure. There's the $CC variable, there's $cc_is_clang, $ac_cv_cc_name, and $GCC. All four of them are used.

#110577 points out that the compiler selection check on macOS is at least partly obsolete. Perhaps that issue deserves to be re-opened and investigated on its own.

$ac_cv_cc_name was introduced by Christian in 3124d9a (PR: #93492, issue: #93491).

[erlend-aasland]

#117815 adapts most relevant checks to use $ac_cv_cc_name. Reviews welcome!