libc: add sys/signal.h for compatibility

Some applications look for sys/signal.h instead of signal.h.
Work around those apps.

Change-Id: I76ac7744ebc56d196b5f0cb9ed381d32817436b9
Add the glibc-compatible names to <sys/endian.h>.

Also remove declarations for functions that don't exist; these
are all macros.

Bug: http://code.google.com/p/android/issues/detail?id=41769
Change-Id: Ia3774ab2ff7d3c535f83774eac61068f9b11e194