Make ncurses build with GCC 5.0 and up

Make ncurses build with GCC 5.0 and up

Merge the end result of two upstream changes:

Original fix from 20141206:
  + modify MKlib_gen.sh to work around change in development version of
    gcc introduced here:
            https://gcc.gnu.org/ml/gcc-patches/2014-06/msg02185.html
            https://gcc.gnu.org/ml/gcc-patches/2014-07/msg00236.html
    (reports by Marcus Shawcroft, Maohui Lei).

Later fixed in different manner in 20150725:
  + use alternate workaround for gcc 5.x feature (adapted from patch by
    Mikhail Peselnik).