runtime/CMakeLists.txt: Use target_include_directories

Otherwise, include directories are not propagated to targets calling
target_link_libraries().

Author: midokura-xavi92

src/runtime/CMakeLists.txt

@@ -1,7 +1,3 @@
-include_directories (
-    "${PROJECT_SOURCE_DIR}/include"
-)
-
 add_library(flatccrt
     builder.c
     emitter.c
@@ -11,6 +7,9 @@ add_library(flatccrt
     json_printer.c
 )
 
+target_include_directories(flatccrt PUBLIC
+    "${PROJECT_SOURCE_DIR}/include")
+
 if (FLATCC_INSTALL)
     install(TARGETS flatccrt DESTINATION ${lib_dir})
 endif()