Add explicit handling of CMAKE_BUILD_TYPE.
Add explicit handling of CMAKE_BUILD_TYPE.

ghisvail/IRTK,BioMedIA/irtk-refactored-deprecated,ghisvail/IRTK,BioMedIA/irtk-refactored-deprecated,BioMedIA/irtk-refactored-deprecated,ghisvail/IRTK