Improve ExternalProject cmake file (#3697)

* Set cmake CMP0144, if available

Signed-off-by: Robert Adam <dev@robert-adam.de>

* Add include dirs directly to defined targets

By directly associating the defined antlr_* targets with the respective
include directories, we make sure that any user that links against one
of these targets, automatically has the necessary directories in their
include path as well (without the need to explicitly specify them) as
cmake will transitively propagate the interface include dirs to the
linked-to target.

Signed-off-by: Robert Adam <dev@robert-adam.de>

runtime/Cpp/cmake/ExternalAntlr4Cpp.cmake

@@ -1,5 +1,9 @@
 cmake_minimum_required(VERSION 3.7)
 
+if(POLICY CMP0114)
+    cmake_policy(SET CMP0114 NEW)
+endif()
+
 include(ExternalProject)
 
 set(ANTLR4_ROOT ${CMAKE_CURRENT_BINARY_DIR}/antlr4_runtime/src/antlr4_runtime)
@@ -11,6 +15,10 @@ if(NOT DEFINED ANTLR4_TAG)
   set(ANTLR4_TAG master)
 endif()
 
+# Ensure that the include dir already exists at configure time (to avoid cmake erroring
+# on non-existent include dirs)
+file(MAKE_DIRECTORY "${ANTLR4_INCLUDE_DIRS}")
+
 if(${CMAKE_GENERATOR} MATCHES "Visual Studio.*")
   set(ANTLR4_OUTPUT_DIR ${ANTLR4_ROOT}/runtime/Cpp/dist/$(Configuration))
 elseif(${CMAKE_GENERATOR} MATCHES "Xcode.*")
@@ -135,6 +143,10 @@ add_library(antlr4_static STATIC IMPORTED)
 add_dependencies(antlr4_static antlr4_runtime-build_static)
 set_target_properties(antlr4_static PROPERTIES
                       IMPORTED_LOCATION ${ANTLR4_STATIC_LIBRARIES})
+target_include_directories(antlr4_static
+    INTERFACE
+        ${ANTLR4_INCLUDE_DIRS}
+)
 
 ExternalProject_Add_Step(
     antlr4_runtime
@@ -152,6 +164,11 @@ add_library(antlr4_shared SHARED IMPORTED)
 add_dependencies(antlr4_shared antlr4_runtime-build_shared)
 set_target_properties(antlr4_shared PROPERTIES
                       IMPORTED_LOCATION ${ANTLR4_RUNTIME_LIBRARIES})
+target_include_directories(antlr4_shared
+    INTERFACE
+        ${ANTLR4_INCLUDE_DIRS}
+)
+
 if(ANTLR4_SHARED_LIBRARIES)
   set_target_properties(antlr4_shared PROPERTIES
                         IMPORTED_IMPLIB ${ANTLR4_SHARED_LIBRARIES})