Make sure DEBUG is defined for debug configurations

CMakeLists.txt

@@ -456,6 +456,7 @@ if(SDL_SHARED)
   add_library(SDL3-shared SHARED)
   add_library(SDL3::SDL3-shared ALIAS SDL3-shared)
   SDL_AddCommonCompilerFlags(SDL3-shared)
+  target_compile_definitions(SDL3-shared PRIVATE "$<$<CONFIG:Debug>:DEBUG>")
   set_property(TARGET SDL3-shared PROPERTY UNITY_BUILD OFF)
   if ("c_std_99" IN_LIST CMAKE_C_COMPILE_FEATURES)
     target_compile_features(SDL3-shared PRIVATE c_std_99)
@@ -468,6 +469,7 @@ if(SDL_STATIC)
   add_library(SDL3-static STATIC)
   add_library(SDL3::SDL3-static ALIAS SDL3-static)
   SDL_AddCommonCompilerFlags(SDL3-static)
+  target_compile_definitions(SDL3-static PRIVATE "$<$<CONFIG:Debug>:DEBUG>")
   set_property(TARGET SDL3-static PROPERTY UNITY_BUILD OFF)
   if ("c_std_99" IN_LIST CMAKE_C_COMPILE_FEATURES)
     target_compile_features(SDL3-static PRIVATE c_std_99)
@@ -480,6 +482,7 @@ if(SDL_TEST_LIBRARY)
   add_library(SDL3_test STATIC)
   add_library(SDL3::SDL3_test ALIAS SDL3_test)
   SDL_AddCommonCompilerFlags(SDL3_test)
+  target_compile_definitions(SDL3_test PRIVATE "$<$<CONFIG:Debug>:DEBUG>")
 endif()
 
 # Make sure SDL3::SDL3 always exists
@@ -1263,6 +1266,7 @@ target_include_directories(SDL_uclibc PRIVATE "${SDL3_BINARY_DIR}/include-config
 target_include_directories(SDL_uclibc PRIVATE "${SDL3_SOURCE_DIR}/src")
 target_include_directories(SDL_uclibc PRIVATE "${SDL3_SOURCE_DIR}/include")
 SDL_AddCommonCompilerFlags(SDL_uclibc)
+target_compile_definitions(SDL_uclibc PRIVATE "$<$<CONFIG:Debug>:DEBUG>")
 sdl_sources(STATIC "$<TARGET_OBJECTS:SDL_uclibc>")
 set_property(TARGET SDL_uclibc PROPERTY UNITY_BUILD OFF)
 if(TARGET SDL3-shared)