include compiler-rt in build-llvm.pl

Reviewed at http://reviews.llvm.org/D5736

The new test cases for ASan fail if the llvm build that is used with LLDB doesn't have compiler-rt (because the resulting compiler then cannot build with -fsanitize=address). Let's include compiler-rt in build-llvm.pl script and make sure we actually *build* it by removing the NO_RUNTIME_LIBS=1 argument used in the make line. After this, the ASan tests pass on a fresh svn checkout.