mempcpy needs a configure test

[clausecker]

Hi there,

Not only glibc and newlib provide mempcpy, so the build fails e.g. on recent FreeBSD due to a duplicate function mempcpy. To fix this, I've written a patch that adds a configure test to check for mempcpy, only using your own implementation if it is not available.

Unfortunately your code has a custom config.h header which shadows the config.h header generated by autotools. In my patch, I have simply removed the other header and defined the single macro in it elsewhere. Check if that's the solution you want.

[hiSandog]

AC_CHECK_FUNCS([mempcpy]) plus a guarded fallback sounds like the portable direction. Rather than deleting the project's handwritten config.h, could it be renamed to a project-specific header so it cannot shadow the generated Autoconf header? That keeps the existing macro ownership clear and gives FreeBSD and other libc implementations a normal configure-time path.