[CRIU] [PATCH 2/2] make: protobuf -- Fix building, v3

[Filipe Brandenburger]

This is still not fixing the build for me...

I just tried this patch on top of 97743f421c6557 and building from a
clean tree results in:

  PB DDEP  protobuf/stats.proto.d
  PB DEP   protobuf/stats.proto.c.d
make[1]: Leaving directory `/usr/local/google/home/filbranden/devel/criu'
make[1]: Entering directory `/usr/local/google/home/filbranden/devel/criu'
make[1]: Circular protobuf/opts.pb-c.c <- protobuf/opts.pb-c.c
dependency dropped.
make[1]: *** No rule to make target
`protobuf/google.pb-c.cbuf/descriptor.proto', needed by
`protobuf/opts.pb-c.c'.  Stop.
make[1]: Leaving directory `/usr/local/google/home/filbranden/devel/criu'
make: *** [protobuf] Error 2

What seems to be fixing it for me is to remove $(obj)/opts.pb-c.c from
the $(obj)/%.pb-c.c rule introduced in the 97743f421c6557 commit,
since essentially this creates a dependency on itself to build
opts.pb-c.c...

I'll send a patch for it shortly.

Cheers,
Filipe