Right now there is no target in the make files to build just compiler2. To be able to build compiler2 (without also building compiler1) you have to comment out FORCE_TIERED=1 in make/windows/build.make, make/linux/Makefile or make/solaris/Makefile. The make files do "ifdef FORCE_TIERED", so it is not possible to turn it off from the command line.
But if you to that you get compilation errors when compiling src/share/vm/runtime/java.cpp:
D:\clients\brutisso\hotspot_main-rt\src\share\vm\runtime\java.cpp(201) : error C2065: 'C1UpdateMethodData' : undeclared identifier
This is due to java.cpp using compiler1 specific code without #ifdefs.
We need to fix java.cpp so that it can be compiled with just compiler2. Also, I think it would be a good idea to have a separate target for building compiler2 and include that as a build target in JPRT. If we don't test building compiler2 it will stop working again sooner or later.