configure: fix -Wimplicit-function-declaration, -Wimplicit-int

[thesamesam]

Clang 16 makes -Wimplicit-function-declaration and -Wimplicit-int errors by default. Unfortunately, this can lead to misconfiguration or miscompilation of software as configure tests may then return the wrong result.

For more information, see LWN.net [0] or LLVM's Discourse [1], the Gentoo wiki [2], or the (new) c-std-porting mailing list [3].

[0] https://lwn.net/Articles/913505/ [1] https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213 [2] https://wiki.gentoo.org/wiki/Modern_C_porting [3] hosted at lists.linux.dev.

Followup to 6414681ae99d6a0f460f827648f114aa3cb2e419.

Signed-off-by: Sam James sam@gentoo.org

[thesamesam]

Sorry for missing this before. To be clear, the previous commit was fine, just incomplete.

[aoshiken]

Don't worry Sam, you've been very helpful.

Thanks a lot, guy!

[thesamesam]

Thank you!