Avoid duplicating information by using the Msgpack_FIND_VERSION variable
exported by find_package() inside FindMsgpack's pkg_search_module call.

By default, find_library() searches all directories for one possible
name and then looks for the next name.  To make sure we're building
against the same headers and libraries, look for all names in a
directory before moving to the next one.

In 33bc332, version constraints were added to pkg_search_module(), but
that only affects the set of directories searched by
find_library()/find_path().

Once the header directory is found, parse the version from
version_master.h so it can be checked by the find_package() call in the
root CMakeLists.txt.

Neovim's code relies on functionality introduced in msgpack-c 1.0.0
(at least MSGPACK_OBJECT_FLOAT enum value), so enforce that minimum
version.

libmsgpack was the old C++ library provided by msgpack-c.  The C library
is libmsgpackc.

The C++ support became header-only, but there was a bug
(msgpack/msgpack-c#395) wherein using msgpack-c's CMake build system
would only install libmsgpack instead of libmsgpackc.

Searching for both libraries, but preferring libmsgpackc, allows for
building against older msgpack-c releases and prepares for the upcoming
msgpack-c release which fixes the aforementioned issues.

Signed-off-by: James McCoy <jamessan@jamessan.com>

When building for X86 the CMake check_library_exists always fails to find
functions from the Win32 API due to name mangling conventions. The convention
for API functions is __stdcall and the CMake test code assumes __cdecl. Since
these are libraries from the Windows API we can simply link against the
libraries without checking for the functions.

Source: https://github.com/mpeterv/luacheck
Docs:   http://luacheck.readthedocs.org/en/0.12.0/index.html

Run via "make testlint".

I don't want anyone getting the idea that the `-X` flag they might have
used has anything to do with why the `+` is working for them

Before this change, building Neovim would recursively search parent
directories for a .git directory. If Neovim was downloaded as a tarball
(i.e. without a .git directory), but placed in a subdirectory of
a Git repository, this caused a CMake error. Such a situation could
occur when packaging Neovim, for example.

Unfortunately, the previous attempt in #3317 did not fix this problem.