package/python: add optional support for libintl

package/python: add optional support for libintl

Python links to gettext when available:

$ output/host/usr/bin/i586-buildroot-linux-uclibc-readelf -a output/target/usr/lib/python2.7/lib-dynload/_locale.so | grep NEEDED
 0x00000001 (NEEDED)                     Shared library: [libintl.so.8]
 0x00000001 (NEEDED)                     Shared library: [libpython2.7.so.1.0]
 0x00000001 (NEEDED)                     Shared library: [libc.so.0]

In comparison the same library compiled without gettext:

$ output/host/usr/bin/i586-buildroot-linux-uclibc-readelf -a output/target/usr/lib/python2.7/lib-dynload/_locale.so | grep NEEDED
 0x00000001 (NEEDED)                     Shared library: [libpython2.7.so.1.0]
 0x00000001 (NEEDED)                     Shared library: [libc.so.0]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>