$ make -f Makefile
protoc-c --c_out=. proto/Mumble.proto
[libprotobuf WARNING google/protobuf/compiler/parser.cc:547] No syntax specified for the proto file: proto/Mumble.proto. Please use 'syntax = "proto2";' or 'syntax = "proto3";' to specify a syntax version. (Defaulted to proto2 syntax.)
cc -c -I. -fPIC -shared -o proto/Mumble.o proto/Mumble.pb-c.c
In file included from proto/Mumble.pb-c.c:9:0:
./proto/Mumble.pb-c.h:7:10: fatal error: protobuf-c/protobuf-c.h: No such file or directory
 #include <protobuf-c/protobuf-c.h>
          ^~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
Makefile:19: recipe for target 'proto/Mumble.o' failed
make: *** [proto/Mumble.o] Error 1