Remove unnecessary uses of NOT_IN_libc

If a IS_IN_* macro is defined, then NOT_IN_libc is always defined,
except obviously for IS_IN_libc.  There's no need to check for both.
Verified on x86_64 and i686 that the source is unchanged.

       * include/libc-symbols.h: Remove unnecessary check for
       NOT_IN_libc.
       * nptl/pthreadP.h: Likewise.
       * sysdeps/aarch64/setjmp.S: Likewise.
       * sysdeps/alpha/setjmp.S: Likewise.
       * sysdeps/arm/sysdep.h: Likewise.
       * sysdeps/i386/setjmp.S: Likewise.
       * sysdeps/m68k/setjmp.c: Likewise.
       * sysdeps/posix/getcwd.c: Likewise.
       * sysdeps/powerpc/powerpc32/setjmp-common.S: Likewise.
       * sysdeps/powerpc/powerpc64/setjmp-common.S: Likewise.
       * sysdeps/s390/s390-32/setjmp.S: Likewise.
       * sysdeps/s390/s390-64/setjmp.S: Likewise.
       * sysdeps/sh/sh3/setjmp.S: Likewise.
       * sysdeps/sh/sh4/setjmp.S: Likewise.
       * sysdeps/unix/alpha/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/aarch64/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/i386/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/ia64/setjmp.S: Likewise.
       * sysdeps/unix/sysv/linux/ia64/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/sh/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/sparc/sparc32/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/sparc/sparc64/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/tile/sysdep.h: Likewise.
       * sysdeps/unix/sysv/linux/x86_64/sysdep.h: Likewise.
       * sysdeps/x86_64/setjmp.S: Likewise.
Remove redundant CPPFLAGS for some programs

These programs get the NOT_IN_libc twice, once through the 'other'
target and another explicitly.  Remove the explicitly added CPFLAG.

	* catgets/Makefile (CPPFLAGS-gencat): Remove.
	* iconv/Makefile (CPPFLAGS-iconv_prog): Likewise.
	(CPPFLAGS-iconvconfig): Likewise.
	* timezone/Makefile (CPPFLAGS-zic): Likewise.
Remove NOT_IN_libc definition for pthread_atfork

pthread_atfork is already built in an extra-libs context, which gives
it NOT_IN_libc in its CPPFLAGS.  Adding the same definition to CFLAGS
is pointless.

Verified that the code is unchanged on x86_64.