Fix Java core-models build script

This fixes two problems with the core-models build script:

1. Use of add_library with target_source_files listing the same source
   led to including the *source* files along with every build target, hence
   multiple builds of the same file

2. Using add_custom_command to create a pre-build hook instead of a normal
   file-producing command meant java_class_loader.cpp and its dependencies were
   rebuilt on every build.

Author: smowton

src/java_bytecode/CMakeLists.txt

@@ -7,7 +7,6 @@ add_subdirectory(library)
 
 add_library(java_bytecode ${sources} ${headers} )
 add_dependencies(java_bytecode core_models_files)
-target_sources(java_bytecode PUBLIC ${sources} ${headers})
 
 generic_includes(java_bytecode)
 

src/java_bytecode/library/CMakeLists.txt

@@ -4,16 +4,13 @@ set(CMAKE_JAVA_COMPILE_FLAGS -sourcepath "src" -d "classes" -XDignore.symbol.fil
 file(GLOB_RECURSE java_sources "*.java")
 set(JAR_NAME "core-models")
 add_jar(${JAR_NAME} ${java_sources})
-get_filename_component(CORE_MODELS_JAR "core-models.jar" REALPATH BASE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
+get_filename_component(CORE_MODELS_JAR "core-models.jar" REALPATH BASE_DIR ${CMAKE_CURRENT_BINARY_DIR})
 get_filename_component(JAVA_CORE_MODELS_INC "java_core_models.inc" REALPATH BASE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
-file(GLOB_RECURSE jars "*.jar")
 add_executable(java-converter converter.cpp)
 
-add_custom_target(core_models_files)
-add_dependencies(core_models_files ${JAR_NAME})
-add_custom_command(TARGET core_models_files
-                   PRE_BUILD
-                   COMMAND java-converter JAVA_CORE_MODELS core-models.jar > ${JAVA_CORE_MODELS_INC}
-                   )
+add_custom_command(OUTPUT ${JAVA_CORE_MODELS_INC}
+                   COMMAND java-converter JAVA_CORE_MODELS ${CORE_MODELS_JAR} > ${JAVA_CORE_MODELS_INC}
+                   MAIN_DEPENDENCY ${CORE_MODELS_JAR})
 
-set_source_files_properties("java_core_models.inc" GENERATED)
+add_custom_target(core_models_files
+                  DEPENDS ${JAVA_CORE_MODELS_INC})