c99-port branches in dist-git

[Florian Weimer]

I'm going to push a branch to dist-git for very few packages (so far gcc
and redhat-rpm-config) which will be used by COPR builds to port Fedora
to C99 and later language standards.

GCC 14 is expected to reject certain constructs that were removed from C
in C99:

  * implicit function declarations
  * implicit ints
  * implicit conversion between pointers and int
    (that may not have been in C89 even; details still pending)

It's possible to build with -std=gnu89 or -std=c89 to re-enable these
constructs, or fix the sources not to use them.  Implicit function
declarations in particular have wasted countless programmer hours due to
difficult-to-track-down ABI mismatches, so it's definitely desirable to
cause them to fail the build.

We have tooling that identifies these constructs if GCC is used, even if
they are used in configure check.  Unexpected failures in configure
checks can be tricky because if the package is well-written, the end
result is still a consistent build with some expected failures missing,
corresponding testsuite bits disabled etc.

We will contribute fixes upstream and to rawhide, either by fixing the
sources or switch to C89 mode where it is unlikely source changes will
be acceptable to upstream.  The c99-port dist-git branch will only be
used for our support tooling that should not be used by production
builds in the rawhide buildroot.  As this is necessarily a
cross-distribution effort, there will be some tracking mechanism to
record and share patches for which no active upstream exists anymore.

C++ packages are only affected in so far as they use the C compiler in
configure checks: these constructs haven't been part of C++ for a long,
long time and may not have been implemented in G++, ever.

I hope to submit a formal Fedora 40 change proposal after some initial
experiments.

Thanks,
Florian