Improve setting the default build type
Improve setting the default build type

The CMAKE_BUILD_TYPE variable is a CACHE variable
and should be set in a way that persists and is
documented in the CACHE.  Also set the default
values for the gui to ease selection of types.

These changes provide better support for GUI
configurators that support cmake.

Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd