Re: [PATCH] Don’t use AC_EGREP_CPP if affected by CFLAGS

[Bruno Haible]

Hi Paul,

This patch is not good, IMO.

> Without this patch, ‘./configure CFLAGS="-m32"’ fails on gzip with GNU/Linux 
> x86-64.

We have documented in
  
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Preset-Output-Variables.html
that this is the wrong way to do a 32-bit build on 64-bit platforms. There are
two ways that work:
  1) ./configure CC="gcc -m32"
  2) ./configure CPPFLAGS="-m32" LDFLAGS="-m32"

This configuration issue comes up occasionally, therefore it is a documentation
problem that we should probably fix in the INSTALL file.

I'd would be in favour of reverting this change because
  1) AC_COMPILE_IFELSE is slower than AC_EGREP_CPP, and there is common
     consensus (discussion on gnu-prog-discuss in October 2016) that configure
     scripts are already slower than it should be.
  2) There are many more uses of AC_EGREP_CPP outside of gnulib.

Bruno