Clean up <machine/ieee.h>.

The upstream intention was for this to be architecture-dependent, but it's a
lot clearer if we just have one copy.

Change-Id: I4e8310496145f9f411cd2e847c8cd023b1d758e9

Conflicts:
	libc/arch-arm/include/machine/ieee.h
	libc/arch-x86/include/machine/ieee.h
	libc/include/machine/ieee.h