[PR 128] CMake: Fix error including generated protobuf headers

Error was:

| CMake Error in core/storage/ipld/CMakeLists.txt:
|   Target "ipld_node_protobuf"
|   INTERFACE_INCLUDE_DIRECTORIES property contains path:
|
|     "build/core/storage/ipld"
|
|   which is prefixed in the build directory.

Author: eigendude

core/storage/ipld/CMakeLists.txt

@@ -16,7 +16,7 @@ add_library(ipld_node_protobuf
     ${PB_BUILD_DIR}/ipld_node.pb.h
     ${PB_BUILD_DIR}/ipld_node.pb.cc
     )
-target_include_directories(ipld_node_protobuf PUBLIC ${PB_BUILD_DIR})
+target_include_directories(ipld_node_protobuf PUBLIC $<BUILD_INTERFACE:${PB_BUILD_DIR}>)
 target_link_libraries(ipld_node_protobuf
     protobuf::libprotobuf
     )