don't use IMGUI_USER_CONFIG

apparently a specific build of GCC 11.2.0 has a bug which prevents using
defines in #include

CMakeLists.txt

@@ -805,7 +805,6 @@ if (BUILD_GUI)
   list(APPEND USED_SOURCES ${GUI_SOURCES})
   list(APPEND DEPENDENCIES_INCLUDE_DIRS
     extern/imgui_patched
-    extern/imgui_conf
     extern/imgui_patched/backends
     extern/IconFontCppHeaders
     extern/igfd
@@ -877,7 +876,7 @@ else()
 endif()
 
 target_include_directories(furnace SYSTEM PRIVATE ${DEPENDENCIES_INCLUDE_DIRS})
-target_compile_definitions(furnace PRIVATE ${DEPENDENCIES_DEFINES} IMGUI_USER_CONFIG="imconfig_fur.h")
+target_compile_definitions(furnace PRIVATE ${DEPENDENCIES_DEFINES})
 target_compile_options(furnace PRIVATE ${DEPENDENCIES_COMPILE_OPTIONS})
 target_link_libraries(furnace PRIVATE ${DEPENDENCIES_LIBRARIES})
 if (PKG_CONFIG_FOUND AND (SYSTEM_FMT OR SYSTEM_LIBSNDFILE OR SYSTEM_ZLIB OR SYSTEM_SDL2 OR SYSTEM_RTMIDI OR WITH_JACK))

extern/imgui_patched/imgui.h

@@ -52,9 +52,7 @@ Index of this file:
 
 // Configuration file with compile-time options
 // (edit imconfig.h or '#define IMGUI_USER_CONFIG "myfilename.h" from your build system')
-#ifdef IMGUI_USER_CONFIG
-#include IMGUI_USER_CONFIG
-#endif
+#include "imconfig_fur.h"
 #include "imconfig.h"
 
 #ifndef IMGUI_DISABLE