Q:

Is it possible to build protobuf without pthread?

There is a need to use Protocol Buffers on the real-time OS where there is no pthread. I am able to link protobuf statically this way
g++ -g -Wall example.pb.cc example.cc -o example -static -lprotobuf -lpthread

However without pthread I get link errors. Is it possible to configure protobuf to work without pthread?

A:

Not really. See this unresolved issue.
Someone has patched an older protobuf version to not depend on pthreads, see here - which you might take a look at if you really need it, and possibly forward port.
Also note that you're supposed to use pkg_config to get the proper compiler and linker flags when using protobuf, e.g.
pkg-config --cflags protobuf         # compiler flags
pkg-config --libs protobuf           # linker flags

