Make project reconfiguration easier

Update existing definitions header automatically instead of prompting the
user to remove it.

Author: Martchus

cmake/modules/LibraryTarget.cmake

@@ -125,10 +125,11 @@ append_user_defined_additional_libraries()
 option(USE_HEADER_FOR_PUBLIC_COMPILE_DEFINITIONS "writes public compile definitions to a header file" ON)
 set(TARGET_GENERATED_INCLUDE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/include")
 set(TARGET_DEFINITIONS_HEADER "${TARGET_GENERATED_INCLUDE_DIRECTORY}/${META_PROJECT_NAME}-definitions.h")
-if (EXISTS "${TARGET_DEFINITIONS_HEADER}")
-    message(STATUS "Using existing \"${TARGET_DEFINITIONS_HEADER}\" for ${META_PROJECT_NAME}. "
-                   "Remove this file to force re-generation of the resource file.")
-elseif (USE_HEADER_FOR_PUBLIC_COMPILE_DEFINITIONS)
+if (USE_HEADER_FOR_PUBLIC_COMPILE_DEFINITIONS)
+    set(EXISTING_DEFS_FOR_HEADER "none")
+    if (EXISTS "${TARGET_DEFINITIONS_HEADER}")
+        file(READ "${TARGET_DEFINITIONS_HEADER}" EXISTING_DEFS_FOR_HEADER)
+    endif ()
     set(DEFS_FOR_HEADER "")
     foreach (DEF ${META_PUBLIC_COMPILE_DEFINITIONS})
         if (DEF MATCHES "([A-Za-z0-9_]+)=([A-Za-z0-9_ ]+)")
@@ -142,7 +143,11 @@ elseif (USE_HEADER_FOR_PUBLIC_COMPILE_DEFINITIONS)
             set(DEFS_FOR_HEADER "${DEFS_FOR_HEADER}#ifndef ${DEF_NAME}\n#define ${DEF_NAME}${DEF_VALUE}\n#endif\n")
         endif ()
     endforeach ()
-    file(WRITE "${TARGET_DEFINITIONS_HEADER}" "${DEFS_FOR_HEADER}")
+    if (NOT "${DEFS_FOR_HEADER}" STREQUAL "${EXISTING_DEFS_FOR_HEADER}")
+        file(WRITE "${TARGET_DEFINITIONS_HEADER}" "${DEFS_FOR_HEADER}")
+    else ()
+        message(STATUS "Header \"${TARGET_DEFINITIONS_HEADER}\" for ${META_PROJECT_NAME} did not change.")
+    endif ()
 endif ()
 
 # add library to be created, set libs to link against, set version and C++ standard