On glibc and Android's bionic, strerror_r returns char* when _GNU_SOURCE is defined. Add a configure check for this rather than assume glibc is the only libc that behaves this way.
On glibc and Android's bionic, strerror_r returns char* when _GNU_SOURCE is defined. Add a configure check for this rather than assume glibc is the only libc that behaves this way.