To fix conditional selection of the actually available gethostbyname_r
and gethostbyaddr_r, we replace __GLIBC__ with __linux__.  @zenhack
tested this to work with gcc and clang targeting glibc, uclibc, musl,
and bionic.

The proper way to check this is through configure.in.

Erlang does not accept these values, so we return an error in the C
interface rather than letting them through to the Erlang VM, which
rejects the message with a somewhat cryptic "bad external term".

Distribute aclocal.m4, install-sh, config.guess, and config.sub
to applications at build time instead of having multiple identical
copies committed in the repository.

Turns out that isfinite emits a function call and not
an instruction in gcc, this makes estone float arith
about 50-75% slower. finite emits the instruction so
we use that instead.