cmake: fix build

[abouvier]

The slirp library includes <compat/strl.h> but never defines HAVE_STRL. On the other hand libretro-common may be compiled with HAVE_STRL and may rely on the system strlcat/strlcpy functions. This lead to link error because libretro-common is compiled without compat/compat_strl.c while slirp try to use libretro-common strlcat/strlcpy functions.

Use target_link_libraries instead of only target_include_directories, to transmit the definitions of libretro-common to slirp.

[JesseTG]

Thanks for contributing! Could you please retarget this PR against dev instead of main?

While you're at it, could you tell me a bit about the environment you're building melonDS DS on? I don't recall encountering this issue before.

[abouvier]

I'm using this recipe on the default Arch Linux build environment. I guess the files compilation order can mask the error, but you can force the fail with -Wl,-z,defs in LDFLAGS.

strlcat/strlcpy are provided by glibc since version 2.38.

[JesseTG]

The build workflows didn't run for some reason. But if this breaks the build, I'll just revert it and we can try again. Thank you!