25edbe888b generates build-time warning from utf8.c

[jkeenan]

A new build-time warning has begun to appear. Compiling an unthreaded build on Ubuntu Linux 24.04 LTS using gcc-13.3.0 as the compiler, I observe:

cc -c -DPERL_CORE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -std=c99 -O2 -Wall -Werror=pointer-arith -Werror=vla -Wextra -Wno-long-long -Wno-declaration-after-statement -Wc++-compat -Wwrite-strings -Wno-use-after-free utf8.c
utf8.c: In function ‘Perl_utf8_to_uv_msgs_helper_’:
utf8.c:2153:39: warning: ‘uv’ may be used uninitialized [-Wmaybe-uninitialized]
 2153 |                             message = Perl_form(aTHX_ surrogate_cp_format, uv);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
utf8.c:1603:8: note: ‘uv’ was declared here
 1603 |     UV uv;
      |        ^~

Bisection with Devel::Git::MultiBisect with the following invocation:

$ perl ~/bin/perl/warnings-transitions.pl \
        --git_checkout_dir="$GIT_WORKDIR/perl2" \
        --workdir="$HOMEDIR/learn/perl/multisect/testing/gcc" \
        --first=5ae25c7756bbd08831a5a3900da1d60b7ba2c19a  \
        --last=c38b0528658b064c1dfaac6ae7abf1445dc71302

... pointed to the following commit:

commit 25edbe888b0c1e4b668bb874584cb944d98c12d5
Author:     Karl Williamson <khw@cpan.org>
AuthorDate: Fri Nov 22 15:23:43 2024 -0700
Commit:     Karl Williamson <khw@cpan.org>
CommitDate: Wed Dec 4 05:47:20 2024 -0700

    utf8_to_uv_msgs: Move premature setting to later

@khwilliamson, can you take a look? Thank you very much.