Log Message:
devel/php-gettext: Fix break caused by gettext-lib change

php-gettext previously searched the $PREFIX/include, /usr/local/include
and /usr/include for the libintl.h header.  The recent change to
gettext-lib moved the header to $PREFIX/include/gettext broke the
build on platforms that don't have native libintl.

Fix this by changing the search path from $PREFIX/include to
$BUILDLINK_DIR/include and let the buildlink system provide the
header.  The core issue is how the configuration script determines if
gettext is available on the system.

No revbump needed; the same gettext-lib is used as before.