cmake --build: Use a default parallel jobs if the `--parallel 0` was passed

Problem description

Just for now, CMake partially support of cmake --build --parallel for calling native tool concurrency.

We aren't talking about passing the specific concurrency value, such as 1 or 42. Just about giving chance to the native tool to determine the concurrency.

There are some cases how we can set the build concurrency just for now:

• From the CLI: cmake --build --parallel - it works
• From the environment variable CMAKE_BUILD_PARALLEL_LEVEL:
  • on Windows via set CMAKE_BUILD_PARALLEL_LEVEL= call - doesn't work
  • on Linux via export CMAKE_BUILD_PARALLEL_LEVEL= - doesn't tested, shouldn't also work
• From the CMakePresets.json file:
  • via the jobs parameter - doesn't possible, because it requires a number, 0 value doesn't work
  • via CMAKE_BUILD_PARALLEL_LEVEL environment variable (environment section) with "" (empty) value - doesn't work
  • via CMAKE_BUILD_PARALLEL_LEVEL environment variable (environment section) with null (JSON null, not the string) value - doesn't work

So, we can set it only by manual pass --parallel argument to the CMake, nothing else.

Test environment

• Windows 10 22H2 x64
• Visual Studio 17 2022 generator
• Native compiling (x64 to x64)

Proposal

Just to use 0 value for this case. It is not acceptable value for now, but we can reserve & use it for running native tool concurrency.