The only way these get used is when you choose to include epoxy/gl.h
but EGL/egl.h.  I'm not sure that's something I want to actually
support, but piglit happened to do so, and this gets things working.

There's not as much support here as in real khrplatform.h, but then
there's no EGL for windows.  And seriously, compilers support 64-bit
and float types, why would you even build this complexity?

Like some of the other missing '\n's, I'd originally used errx(), then
just done a sed job to fprintf when I found that win32 lacked errx().

This should avoid any differences we might end up with compared to
system khrplatform.h.

One of the problems with krhplatform.h (besides it being a terrible
idea in the first place) is that it's not present on many systems at
all, including apple, win32, and linux before late 2009.

So, unless we introduce the first ./configure dependency to the core
library build, we really do need to define these standard types to
their standard values.  But if we allow khrplatform.h inclusion as
well, we'll get long-vs-int redefinition warnings on 32-bit.  So, we
have to completely replicate the header, which is a thing we've done
for everything else except for eglplatform.h.

A testcase will be used to make sure that our types don't drift from
the system khrplatform.h types, if it even exists.

Fixes #17