Building with PKG_CONFIG_PATH set to already-installed previous version fails

[LourensVeen]

If you build MUSCLE3, install it to a directory muscle3/, then add muscle3/lib/pkgconfig to your PKG_CONFIG_PATH environment variable, and then try to build a new version of MUSCLE3, then it will detect the protobuf and gRPC installed by the previous build, but fail to build against it, saying

In file included from muscle3_source/muscle3-0.4.0/libmuscle/cpp/build/muscle_manager_protocol/../../src/muscle_manager_protocol/muscle_manager_protocol.pb.cc:4:0:
muscle3_source/muscle3-0.4.0/libmuscle/cpp/build/muscle_manager_protocol/../../src/muscle_manager_protocol/muscle_manager_protocol.pb.h:10:40: fatal error: google/protobuf/port_def.inc: No such file or directory
 #include <google/protobuf/port_def.inc>
                                        ^
compilation terminated.
make[3]: *** [muscle_manager_protocol.pb.o] Error 1
make[3]: *** Waiting for unfinished jobs....

Probably the headers for protobuf/gRPC aren't installed. We should either install them (or fix the installation), or make it so that MUSCLE3 detects that it cannot compile against this package and build the dependencies locally.

[LourensVeen]

Or remove gRPC/Protobuf.

[LourensVeen]

gRPC/Protobuf removed in 0.5.0.