protobuf-c fails to build with protobuf 3.6

[   38s] + make
[   38s]   CXX      protoc-c/protoc_gen_c-c_bytes_field.o
[   38s] In file included from ./protoc-c/c_bytes_field.h:68,
[   38s]                  from protoc-c/c_bytes_field.cc:63:
[   38s] ./protoc-c/c_field.h:120:3: error: 'scoped_array' does not name a type; did you mean 'sched_param'?
[   38s]    scoped_array > field_generators_;
[   38s]    ^~~~~~~~~~~~
[   38s]    sched_param
[   39s] make: *** [Makefile:1363: protoc-c/protoc_gen_c-c_bytes_field.o] Error 1
[   39s] error: Bad exit status from /var/tmp/rpm-tmp.W8erdV (%build)

CC @jengelh protobuf-c's maintainer

waiting for protobuf-c fix

@dimstar_suse, @factory-repo-checker: review reminder