cmake: Simplify capnp include handling

Stop using lower level target_include_directories to add
CAPNP_INCLUDE_DIRECTORY includes. This is no longer needed now that newer
capnproto releases provide targets that set their own includes.

This change is based on some similar cleanups originally implemented by
Cory Fields <[email protected]> in
#141

Author: ryanofsky

CMakeLists.txt

@@ -53,8 +53,8 @@ capnp_generate_cpp(MP_PROXY_SRCS MP_PROXY_HDRS include/mp/proxy.capnp)
 add_library(mputil OBJECT src/mp/util.cpp)
 target_include_directories(mputil PRIVATE
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-  $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/include>
-  ${CAPNP_INCLUDE_DIRECTORY})
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/include>)
+target_link_libraries(mputil PUBLIC CapnProto::kj)
 
 # libmultiprocess.a runtime library
 set(MP_PUBLIC_HEADERS
@@ -93,8 +93,7 @@ add_library(Libmultiprocess::multiprocess ALIAS multiprocess)
 target_include_directories(multiprocess PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/include>
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
-  ${CAPNP_INCLUDE_DIRECTORY})
+  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 target_link_libraries(multiprocess PUBLIC CapnProto::capnp)
 target_link_libraries(multiprocess PUBLIC CapnProto::capnp-rpc)
 target_link_libraries(multiprocess PUBLIC CapnProto::kj)