Meson now propagates its build type to CMake

When the CMake build type variable, CMAKE_BUILD_TYPE, is not set via the add_cmake_defines method of the cmake options object, it is inferred from the Meson build type. Build types of the two build systems do not match perfectly. The mapping from Meson build type to CMake build type is as follows:

• debug -> Debug
• debugoptimized -> RelWithDebInfo
• release -> Release
• minsize -> MinSizeRel

No CMake build type is set for the plain Meson build type. The inferred CMake build type overrides any CMAKE_BUILD_TYPE environment variable.