Fix CC logic in configure

[thesamesam]

In e9a52aa,
the logic was changed to try check harder for GCC, but it dropped
the default setting of cc=${CC}. It was throwing away any pre-set CC value as
a result.

The rest of the script then cascades down a bad path because it's convinced
it's not GCC or a GCC-like compiler.

This led to e.g. misdetection of inability to build shared libs
for say, multilib cases (w/ CC being one thing from the environment being used
for one test (e.g. x86_64-unknown-linux-gnu-gcc -m32 and then 'cc' used for
shared libs (but missing "-m32"!)). Obviously just one example of how
the old logic could break.

This restores the old default of 'CC' if nothing overrides it later
in configure.

Bug: https://bugs.gentoo.org/836308
Signed-off-by: Sam James sam@gentoo.org

[thesamesam]

@madler Could you take a look at this as well as #229 and #599 please? It'd be a big help for distributions who will all be rushing to update soon.

Thanks for the new release.

[ncopa]

I can confirm that this PR solve #608

[aeiouaeiouaeiouaeiouaeiouaeiou]

This also fixes the compilation of dynamic library in macOS.

[madler]

See 05796d3 .

[thesamesam]

Thanks.

[Neustradamus]

@madler: It is not possible to merge PRs than close?
I think that it is better to have contributor commits...

[madler]

Not sure how.

[thesamesam]

Not sure how.

I use pram usually (e.g. pram https://github.com/madler/zlib/pull/607), but alternatively:

1. wget https://github.com/madler/zlib/pull/607.patch -O /tmp/patch-to-review.patch
2. Review /tmp/patch-to-review.patch
3. git am /tmp/patch-to-review.patch to apply.

(github has its own merge buttons but I don't usually use those as the repo isn't always hosted on github directly, just a mirror.)

[ncopa]

Not sure how.

github normally have a green "merge" button, if you don't care about the merge commits.

Otherwise a shortcut of @thesamesam's suggestion:
curl -L https://github.com/madler/zlib/pull/607.patch | git am -3

[leahneukirchen]

A convenient way also provided by https://github.com/leahneukirchen/git-merge-pr :)