libc/glibc: do not try to download NPTL add-on

The NPTL add-on has always been internal, so there is no
reason to try downloading it, it will never succeed.
Add provision to skip other add-ons as well.

For consistency, do the same test in both glibc and eglibc.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 #!/bin/sh

 # Needed for systems without gettext

 $* -xc -o /dev/null - > /dev/null 2>&1 << EOF

 #include <libintl.h>

 int main()

 {

 	gettext("");

 	return 0;

 }

 EOF

 if [ ! "$?" -eq "0"  ]; then

 	echo -DKBUILD_NO_NLS;

 fi