gh-112301: fix compiler warning about a possible use of an uninitialized variable

[carsonRadtke]

In #112301, @mdboom posted a proposal for adding some recommended compiler flags.

This PR addresses a single class of warnings (-Wmaybe-uninitialized) that may crop up if we were to switch to the "hardened" build command.

Specific build error:

./Modules/_io/fileio.c:175:9: warning: ‘exc’ may be used uninitialized [-Wmaybe-uninitialized] 175 | _PyErr_ChainExceptions1(exc); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ ./Modules/_io/fileio.c: In function ‘_io_FileIO_close’: ./Modules/_io/fileio.c:160:15: note: ‘exc’ was declared here 160 | PyObject *exc; 

• Issue: Consider applying flags for warnings about potential security issues #112301

[ghost]

All commit authors signed the Contributor License Agreement.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[sethmlarson]

Should we be adding the -Wmaybe-uninitialized option to the build in this PR as well? I think that's coming from -Wall but it's unlikely we enable that option in particular?

[mdboom]

Should we be adding the -Wmaybe-uninitialized option to the build in this PR as well? I think that's coming from -Wall but it's unlikely we enable that option in particular?

Alternatively, should we be adding -Werror=maybe-uninitialized which would error if this kind of thing ever crept back in? IMHO, warnings almost always just get ignored. I'm pretty comfortable that this warning is just a bunch of false positives that are hard to fix. On the other hand, we should probably build consensus before adding new error types. (Probably a discussion to have in the general sense over on #112301).