ncurses 6.0 - patch 20180106

ncurses 6.0 - patch 20180106

+ fixes for writing extended color pairs in putwin.
+ modify test/savescreen.c to add test patterns that exercise 88-,
  256-, etc., colors.
+ modify configure option --with-build-cc, adding clang, c89 and c99
  as possible default values.
+ modify ncurses-examples configure script to use pkg-config for the
  extra form/menu/panel libraries, to be more consistent with the
  handling of the curses/ncurses library.
+ modify test-packages for mingw to supply "pc" files.
+ modify gen-pkgconfig.in to list -lpthread as a private library when
  configured to access it via weak symbols.
+ simplify gen-pkgconfig.in, adding -ltinfo without the special linker
  checks because some versions of the linker simply hard-code the
  behavior.
+ update URLs for ncurses website to use https.
+ modify CF_CURSES_LIBS to fill in $cf_nculib_root in case the
  ncurses-examples are built with a system ncurses that lacks the
  standard "curses" symbolic link, as done by SuSE.  The symbol is
  needed to make a followup check for the pthread library work, and
  would be set properly using the options "--with-screen", etc.
+ generate misc/*.pc with "all" rule, as done for "sources" rule
  (report by Jeffrey Walton).