package/ncmpc: fix build without NLS

package/ncmpc: fix build without NLS

The build fails if libintl.h is found but xgettext is not available:

Has header "libintl.h" : YES
Library intl found: NO

po/meson.build:28:5: ERROR: Can not do gettext because xgettext is not installed.

This is because enable_nls defaults to true if libintl.h is found. Use
the nls option to enable/disable NLS explicitly, depending on
BR2_SYSTEM_ENABLE_NLS,

Also, fix the second patch to always look for libintl, even if NLS is
not enabled. The enable_nls option disables processing the po files, but
the gettext calls in the source are still there, so we need to link with
libintl anyway.

Fixes:
 - http://autobuild.buildroot.org/results/0ab0a42fd4c5c9fd5891f3b84287bd788f763ba4

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>