Merge branch 'pkg-config-ncursesw' into 'master'

configure.ac: use pkg-config to get ncursesw header location

Don't assume ncursesw headers are in ../usr/include/ncursesw/..
On a pure build/system without legacy ncurses that may not be true.
Since we're using pkg-config let it provide the correct include path.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
See merge request !23