build-sys: prefer ncurses-config rather than pkg-config

build-sys: prefer ncurses-config rather than pkg-config

If you have installed:

 ii  libncurses5:i386      5.9+20140913-1+b1  i386   shared libraries for terminal handling
 ii  libncurses5-dev:i386  5.9+20140913-1+b1  i386   developer's libraries for ncurses
 ii  libncursesw5:i386     5.9+20140913-1+b1  i386   shared libraries for terminal handling (wide character support)

then pkg-config blindly follows ncursesw although there are not header
files for this library. It seems better to use pkg-config as fallback
solution only.

Signed-off-by: Karel Zak <kzak@redhat.com>