[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  outdated C4251 suppression, add /utf-8, and use /O2 instead of /Ox.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.

servatrice/check_schema_version.sh

@@ -10,7 +10,7 @@ declare -i schema_ver="${version_line%%)*}"
 latest_migration="$(ls -1 servatrice/migrations/ | tail -n1)"
 xtoysql="${latest_migration#servatrice_}"
 xtoy="${xtoysql%.sql}"
-declare -i old_ver="10#${xtoy%_to_*}" #declare as integer with base 10, numbers with a leading 0 are normally interpreted as base 16
+declare -i old_ver="10#${xtoy%_to_*}" # declare as integer with base 10, numbers with a leading 0 are normally interpreted as base 16
 declare -i new_ver="10#${xtoy#*_to_}"
 
 if ((old_ver >= new_ver)); then