[Build] Clean up CMake compiler flags and CI build script

Compiler flags are applied once and for the right compiler:

- Detect the toolchain by CMAKE_CXX_COMPILER_ID (MSVC / GNU / Clang,
  warn on an unknown one).
- MSVC: drop /std:c++20 (CMAKE_CXX_STANDARD already adds it) and the
  outdated C4251 suppression, add /utf-8, and use /O2 instead of /Ox.
- GCC: drop the no-op -Wno-long-long and the macOS-only -std=gnu++20
  override; CMAKE_CXX_EXTENSIONS=OFF now owns the dialect.
- Use add_compile_definitions for SFMT_MEXP instead of add_definitions.

CI build script:

- Only run the schema version check for server builds.
- Accept boolean env flags as 1 and say so in the header.
- Print ccache, ctest and cpack versions next to their log groups.
- Only build the macOS vcpkg triplet when vcpkg is actually used.
- Drop the extra cmake --build verbosity.
- Install NSIS without chocolatey progress noise.

.github/workflows/desktop-build.yml

@@ -757,7 +757,7 @@ jobs:
       - name: "[Windows] Install NSIS"
         if: matrix.os == 'Windows'
         shell: bash
-        run: choco install nsis
+        run: choco install nsis --no-progress
 
       # Ninja invokes cl.exe directly and needs the MSVC environment on PATH.
       - name: "[Windows] Set up MSVC environment"