Bring our <machine/endian.h> files back in sync.

They'd drifted slightly which led to a compilation error in toybox,
which was assuming pid_t was defined. arm and arm64 were picking it
up via <endian.h> but x86 wasn't.

Change-Id: I58401e6c0066959dfc3b305b020876aaf7074bbf
Merge "Bring our <machine/endian.h> files back in sync."