Fix alpine

[reaperhulk]

Fixes compilation on alpine linux and cleans up a bunch of warnings that can occur on platforms that don't use glibc.

[lvh]

You know what's BSD? Literally everything.

[lvh]

LGTM modulo comments

[lvh]

I have found the musl entry about this:

http://wiki.musl-libc.org/wiki/FAQ#Q:_I.27m_trying_to_compile_something_against_musl_and_I_get_error_messages_about_sys.2Fcdefs.h

Should we just use the libsodium-style:

#ifdef __cplusplus
extern "C" {
#endif

and

#ifdef __cplusplus
}
#endif

If this is in the bcrypt code from OpenBSD, I'm surprised to find things that use glibc internals there.

[lvh]

(I know you mentioned never using a C++ compiler, but hopefully we can preempt unnecessary problems for people who end up doing that by accident.)

[reaperhulk]

I'm okay with switching this. Hopefully that works in VS2008 as well :)

[lvh]

Not sure if Travis is being hilariously slow or is just broken.

[lvh]

I have cancelled and restarted the build.

[reaperhulk]

Travis's mac builders are completely dead and have been all day. Canceling won't help. We get to wait :(

[lvh]

None of the other builders did anything though; they were all stuck in yellow.