Meet the following compiler error:
/mnt/trace-tools/eBPF/bcc/src/cc/frontends/clang/b_frontend_action.cc:
In member function bool
ebpf::BTypeVisitor::VisitVarDecl(clang::VarDecl*):]
/mnt/trace-tools/eBPF/bcc/src/cc/frontends/clang/b_frontend_action.cc:1449:18:
error: BPF_MAP_TYPE_RINGBUF was not declared in this scope; did you mean
BPF_MAP_TYPE_QUEUE?
1449 | map_type = BPF_MAP_TYPE_RINGBUF; | ^~~~~~~~~~~~~~~~~~~~ |
     BPF_MAP_TYPE_QUEUE
make[2]: ***  [src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/build.make:95:
rc/cc/frontends/clang/CMakeFiles/clang_frontend.dir/b_frontend_action.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:1065: src/cc/frontends/clang/CMakeFiles/clang_frontend.dir/all] Error 2
make: *** [Makefile:160: all] Error 2

This because, submodule libbpf can't sync when do cmake.
So enlarger the sync contion: only submodule is clean, we do sync
submodle when do cmake.

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>