ncurses 6.0 - patch 20150912

+ fixes for configure/build using clang on OSX (prompted by report by
  William Gallafent).
  + do not redefine "inline" in ncurses_cfg.h; this was originally to
    solve a problem with gcc/g++, but is aggravated by clang's misuse
    of symbols to pretend it is gcc.
  + add braces to configure script to prevent unwanted add of
    "-lstdc++" to the CXXLIBS symbol.
  + improve/update test-program used for checking existence of stdc++
    library.
  + if $CXXLIBS is set, the linkage test uses that in addition to $LIBS