Can no longer build libc stdio without math.h

[antmerlino]

I had a very simple configuration for a board that worked at some point and I ran into build errors because it was looking for math.h and I didn't have CONFIG_LIBM on.

Looks like this change d17b963 moved types and subsequent includes.

Do we want to fix this, or do we want to require that users provide a math.h, either via CONFIG_LIBM, toolchain, or otherwise?

If we did want to fix, I think we need to:

1. guard every place in libc that uses float/double with CONFIG_LIBC_FLOATINGPOINT
2. guard the include with either CONFIG_LIBC_FLOATINGPOINT or CONFIG_LIBM