The only thing this affected was the return value of
has('browsefilter').

* Hide commit information from --version if we can't find any (e.g. when
  building from tarball).

To define a release in CMake, set NVIM_VERSION_PRERELEASE to "".
This will modify --version output to:

    * Show annotated Git tag instead of commit hash (NVIM_VERSION_COMMIT).
    * Hide commit date (NVIM_VERSION_BUILD).

RETSIGTYPE, SIGRETURN, and SIGDEFARG are always defined the same, so
inline them for simplicity; SIGDUMMYARG, however, is unused, so remove
it.

Even if these things don't work on windows, the signal handler in
if_cscope.c is already wrapped with '#idef UNIX', as is its only call
site.

Reviewed-by: Justin M. Keyes <justinkz@gmail.com>

HAVE_SYS_TIME_H isn't being used by anything, remove it.

Since gettimeofday() was replaced by os_time in
fb5a786bdb5b7b52b9c36b3eb8b6d2cc002aa8f3 we do not need sys/time.h.

Removed unneeded platform checks from config/config.h.in and
config/CMakeLists.txt

- HAVE_OSPEED and HAVE_UP_BC_PC were used by the old UI, and are
  no longer needed.
- sigvec() was used as part of the signal handling code in os_unix.c, but it is
  no longer used in Neovim.
- The function lstat() is no longer used, replaced with libuv.