ncurses 6.2 - patch 20200229

ncurses 6.2 - patch 20200229

+ modify CF_NCURSES_CONFIG to work around xcode's c99 "-W" option,
  which conflicts with conventional use for passing linker options.
> fixes for building with Visual Studio C++ and msys2 (patches by
  "Maarten Anonymous"):
+ check for pcre2posix.h instead of pcre2-posix.h
+ add case in CF_SHARED_OPTS for msys2 + msvc
+ add fallback definition for STDIN_FILENO in progs.priv.h
+ modify win_driver.c to use _alloca() rather than gcc's variable
  length array feature.
+ add NCURSES_IMPEXP to ncurses wrapped-variable declarations
+ remove NCURSES_IMPEXP from class variables in c++/cursslk.h
+ remove fallback prototype for exit() from c++/etip.h.in
+ use configured check for <sys/time.h> in a couple of places
+ conditionally include winsock.h in ncurses/win32con/gettimeofday.c,
  because Visual Studio needs this for the timestruct declaration.
+ adjust syntax in a couple of files using the NCURSES_API symbol.