Fix usage of CMAKE_BUILD_TYPE setting
Fix usage of CMAKE_BUILD_TYPE setting

The build type was set to Release in the top level cmake file.
This was a rather confusing behaviour, as one would expect to
be able to easily debug the code after using `cmake -DCMAKE_BUILD_TYPE=Debug`.

iovisor/bcc,iovisor/bcc,brendangregg/bcc,mcaleavya/bcc,iovisor/bcc,iovisor/bcc,mcaleavya/bcc,brendangregg/bcc,tuxology/bcc,tuxology/bcc,tuxology/bcc,mcaleavya/bcc,mcaleavya/bcc,romain-intel/bcc,brendangregg/bcc,tuxology/bcc,romain-intel/bcc,brendangregg/bcc,iovisor/bcc,romain-intel/bcc,romain-intel/bcc,brendangregg/bcc,romain-intel/bcc,tuxology/bcc,mcaleavya/bcc