Use `-ffile-prefix-map` for relative `__FILE__`

Fixes #4420

CMake/functions/devilutionx_library.cmake

@@ -1,4 +1,5 @@
 include(functions/genex)
+include(functions/set_relative_file_macro)
 
 # This function is equivalent to `add_library` but applies DevilutionX-specific
 # compilation flags to it.
@@ -66,6 +67,8 @@ function(add_devilutionx_library NAME)
   endif()
 
   target_compile_definitions(${NAME} PUBLIC ${DEVILUTIONX_DEFINITIONS})
+
+  set_relative_file_macro(${NAME})
 endfunction()
 
 # Same as add_devilutionx_library(${NAME} OBJECT) with an additional

CMake/functions/set_relative_file_macro.cmake

@@ -0,0 +1,15 @@
+# Sets the __FILE__ macro value to be relative to CMAKE_SOURCE_DIR.
+function(set_relative_file_macro TARGET)
+  if(NOT CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
+    if((CMAKE_CXX_COMPILER_ID MATCHES "CLANG" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 12)
+        OR (CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8))
+      target_compile_options(${TARGET} PUBLIC "-ffile-prefix-map=${CMAKE_SOURCE_DIR}/=")
+    else()
+      get_target_property(_srcs ${TARGET} SOURCES)
+      foreach(_src ${_srcs})
+        set_source_files_properties(${_src} PROPERTIES COMPILE_DEFINITIONS __FILE__="${_src}")
+      endforeach()
+      target_compile_options(${TARGET} PRIVATE -Wno-builtin-macro-redefined)
+    endif()
+  endif()
+endfunction()

CMakeLists.txt

@@ -247,18 +247,8 @@ if(BUILD_TESTING)
   add_subdirectory(test)
 endif()
 
-if(NOT CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
-  # Change __FILE__ to only show the path relative to the project folder
-  get_target_property(libdevilutionx_SRCS ${BIN_TARGET} SOURCES)
-  foreach(SOURCE_FILE ${libdevilutionx_SRCS})
-    set_source_files_properties(${SOURCE_FILE} PROPERTIES
-      COMPILE_DEFINITIONS __FILE__="${SOURCE_FILE}"
-    )
-  endforeach(SOURCE_FILE)
-
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-builtin-macro-redefined")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-builtin-macro-redefined")
-endif()
+include(functions/set_relative_file_macro)
+set_relative_file_macro(${BIN_TARGET})
 
 if(APPLE)
   set_source_files_properties("./Packaging/apple/AppIcon.icns" PROPERTIES MACOSX_PACKAGE_LOCATION Resources)