configure: fix -Wimplicit-function-declaration, -Wstrict-prototypes

[thesamesam]

Clang 16 makes -Wimplicit-function-declaration an error 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.

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

[aoshiken]

Thank you

[thesamesam]

Thanks!