build: various cmake fixes (#21902)

* build: various cmake refactors and simplifications

- Add STATUS keyword to message to ensure messages are shown in the
  correct order.
- Remove DEPS_CXX_COMPILER as we don't rely on C++ for any of our
  dependencies.
- Simplify how msgpack and luv configure options are constructed.
- Rely on the default installation for luv instead of manually passing
  configure, build and install commands.
- Simplify return code conditional.

* build: remove CMAKE_OSX_ARCHITECTURES_ALT_SEP workaround

CMAKE_OSX_ARCHITECTURES_ALT_SEP was defined as a workaround to prevent
the shell from interpreting `;`, which CMake uses as a list separator.
However, the same thing can be achieved by instead passing
CMAKE_OSX_ARCHITECTURES as a cache variable instead, which is a more
idiomatic way of achieving the same thing.

* build: define CMAKE_BUILD_TYPE before adding it to BUILD_TYPE_STRING

The problem with the current setup is that CMAKE_BUILD_TYPE is defined
after BUILD_TYPE_STRING. BUILD_TYPE_STRING will then be empty on the
first run, meaning that dependencies are built without a build type.
However, since CMAKE_BUILD_TYPE is a cache variable its value will
persist in subsequent runs. On the second run BUILD_TYPE_STRING will
have the correct value, but it's a different value from the ones the
dependencies were built with. This will force some dependencies to be
built again.

Fixes https://github.com/neovim/neovim/issues/21672.

cmake/GenerateVersion.cmake

@@ -7,7 +7,7 @@ execute_process(
   OUTPUT_STRIP_TRAILING_WHITESPACE
   RESULT_VARIABLE RES)
 
-if(RES AND NOT RES EQUAL 0)
+if(RES)
   message(STATUS "Using NVIM_VERSION: ${NVIM_VERSION}")
   file(WRITE "${OUTPUT}" "")
   return()