The commands run in cmake script mode (-P) can simply be run in the main
cmake run instead.

It was set in file cmake/i386-linux-gnu.toolchain.cmake which has been
removed since we don't use Travis anymore.

This partially reverts commit 42aeb5c5b18af1362362a2e6bdf10a2a4ec70f0f.

Setting cmake policies is normally not required as
cmake_minimum_required automatically sets these. One exception is cmake
script mode (-P) since it automatically resets all policy changes.

Closes: https://github.com/neovim/neovim/issues/20286

Add --always flag to `git describe` so version generation succeeds if
current directory is in a git repo. If not in git repo, fall back to a
default version in the format vx.y.z-dev

Having cmake version 3.10 as the required minimum version ensures these
are set to new by default.

Change the default build type to always be Debug, and allow only four
predefined build types: Debug, Release, RelWithDebInfo and MinRelSize.
Furthermore, flags meant for single-configuration generator (make,
ninja) will not be used for multi-configuration generators (visual
studio, Xcode), and flags meant for multi-configuration generators will
not be used for single-configuration generators.

This will allow Debug builds to be built with MSVC which requires that
all dependencies are also built with the Debug build type to avoid
runtime library mismatch.

The correct way to specify build type (for example Release) for
single-configuration generators (Make and Ninja) is to run

cmake -B build -D CMAKE_BUILD_TYPE=Release
cmake --build build

while for multi-configuration generators (Visual Studio, Xcode and Ninja
Multi-Config) is to run

cmake -B build
cmake --build build --config Release

Passing CMAKE_BUILD_TYPE for multi-config generators will now not only
not be used, but also generate a warning for the user.

Co-authored-by: dundargoc <gocundar@gmail.com>

Co-authored-by: Daniel Hahler <git@thequod.de>

Replace its functionality by copying the entire directory where the
reports are instead.

It was used in .travis.yml which has been removed.

- Use DIRECTORY instead of PATH in get_filename_component
- Use COMPILE_OPTIONS instead of COMPILE_FLAGS. COMPILE_FLAGS is treated
  as a single string while COMPILE_OPTIONS is a list, meaning that cmake
  will take care of any escaping and quoting automatically.