package/ncurses: Fix GCC 5.x preprocessor failure

package/ncurses: Fix GCC 5.x preprocessor failure

Building ncurses 5.9 with GCC 5.x fails with a syntax error, caused by
earlier preprocessing. This failure is more likely when building for
host (e.g. host-ncurses) that recently updated to GCC 5.x.

This patch is taken from the following link (more information is also
available here):
https://groups.google.com/forum/#!topic/sage-trac/U31shviuqzk

Signed-off-by: Doug Kehn <rdkehn@yahoo.com>
Acked-by: Jaap Crezee <jaap@jcz.nl>
Tested-by: Jaap Crezee <jaap@jcz.nl>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>