Remove C99-obsoleted constructs

See [this development thread for a future Fedora change](https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/CJXKTLXJUPZ4F2C2VQOTNMEA5JAUPMBD/) or [the proposed change page](https://fedoraproject.org/wiki/Changes/PortingToModernC). These may be made stronger errors in GCC 14.

Testing Done:
Configured with `-Dc_args='-Werror=implicit-int -Werror=implicit-function-declaration -Werror=int-conversion -Werror=strict-prototypes -Werror=old-style-definition'` and compiled.

Reviewed at https://reviews.imfreedom.org/r/1973/