Defer to cmake to determine the correct build command.

Instead of presuming the build system is make when generating a cmake project
instead ask cmake to invoke the build system itself.
Patch bzip2 to defer to the system cc compiler.
Merge pull request #149 from robertmaynard/bzip2_clang

Patch bzip2 to defer to the system cc compiler.
Merge pull request #148 from robertmaynard/cmake_build

Defer to cmake to determine the correct build command.