[CMake] setting a default build type

[Brandon J. Van Every]

On MSVC my CMakeLists.txt generates Debug, Release, MinSizeRel, and 
RelWithDebInfo build types.  I want to keep all 4 of 'em.  I want to 
select MinSizeRel as the default build, so that if an end user just 
fires up BUILD_ALL and does nothing else, he'll get a MinSizeRel build.  
The default default is "Debug" and that's not what I want.  So, is there 
a mechanism to specify the default build type?  I was unable to deduce 
it from the docs if there is one.  Seems clear enough how to ship *one* 
build type, I'd just do (SET CMAKE_BUILD_TYPE MinSizeRel).  But I want 
all 4 to be shipped.


Cheers,
Brandon Van Every