Refine build system for efficient configurations

[jserv]

This addresses build system inefficiencies and compatibility issues:

1. Configuration change detection: Use cmp-based comparison to avoid unnecessary rebuilds when configuration hasn't actually changed. Previously, every make run would touch .config and trigger full rebuilds.
2. Directory creation optimization: Replace runtime mkdir -p $(shell dirname) calls with order-only prerequisites (|).
3. Configuration dependency tracking: Add $(CONFIG_FILE) as explicit prerequisite to all compilation rules. This ensures object files rebuild when feature flags change (e.g., ENABLE_JIT=1 -> 0).
4. Build system hygiene: Remove duplicate .PHONY declarations, fix shell script indentation in riscv-arch-test.mk, and add .PHONY coverage for all target declarations.

---

Summary by cubic

Speeds up and stabilizes the Make build by only updating .config when values change and rebuilding objects when feature flags change. Also replaces ad‑hoc mkdir calls with proper directory prerequisites and adds clearer config warnings.

• Refactors

  • Update .config only when config actually changes; remove forced config step from default build.
  • Track $(CONFIG_FILE) in all compile rules (core, dev, tests, tools, softfloat) so files rebuild when flags change.
  • Use order-only prerequisites and explicit dir targets instead of inline mkdir.
  • Add GNU make version check for order-only prerequisites.
  • Clean up .PHONY targets and minor make/script formatting; soften noisy logs (use warnings where appropriate).
  • Add config validation messages (e.g., SDL with SYSTEM/FULL4G, T2C disabled note).

• Migration

  • Requires GNU make 3.81 or newer.

[jserv]

@ChinYikMing, Although we are experiencing intermittent CI regressions on macOS-arm64 targets, it remains essential to refine the build system. Please review the changes, especially those related to WebAssembly-specific rules.

[ChinYikMing]

@jserv , could you point out where is the warnings of music_modplug.c under emcc?

[ChinYikMing]

Running make doom ENABLE_SDL_MIXER=0 -j8 or make system ENABLE_SYSTEM=1 ENABLE_SDL_MIXER=0 INITRD_SIZE=32 -j8 with the changes gives errors:

  CC	build/syscall_sdl.o
src/syscall_sdl.c:108:12: error: ‘chan’ defined but not used [-Werror=unused-variable]
  108 | static int chan;
      |            ^~~~
src/syscall_sdl.c:107:17: error: ‘nr_sfx_samples’ defined but not used [-Werror=unused-variable]
  107 | static uint32_t nr_sfx_samples;
      |                 ^~~~~~~~~~~~~~
src/syscall_sdl.c:98:17: error: ‘music_midi_data’ defined but not used [-Werror=unused-variable]
   98 | static uint8_t *music_midi_data;
      |                 ^~~~~~~~~~~~~~~
src/syscall_sdl.c:97:18: error: ‘music_thread’ defined but not used [-Werror=unused-variable]
   97 | static pthread_t music_thread;
      |                  ^~~~~~~~~~~~
cc1: all warnings being treated as errors
make: *** [Makefile:395: build/syscall_sdl.o] Error 1

Consider this patch for better conditional compile for ENABLE_SDL_MIXER:

diff --git a/src/syscall_sdl.c b/src/syscall_sdl.c
index 32a3397..4f38a1a 100644
--- a/src/syscall_sdl.c
+++ b/src/syscall_sdl.c
@@ -94,15 +94,14 @@ typedef struct sound {
 } sound_t;
 
 /* SDL-mixer-related and music-related variables */
+#if RV32_HAS(SDL_MIXER)
 static pthread_t music_thread;
 static uint8_t *music_midi_data;
-#if RV32_HAS(SDL_MIXER)
 static Mix_Music *mid;
 
 /* SDL-mixer-related and sfx-related variables */
 static pthread_t sfx_thread;
 static Mix_Chunk *sfx_chunk;
-#endif
 static uint8_t *sfx_samples;
 static uint32_t nr_sfx_samples;
 static int chan;
@@ -111,6 +110,7 @@ static int chan;
 static bool audio_init = false;
 static bool sfx_thread_init = false;
 static bool music_thread_init = false;
+#endif
 
 typedef struct {
     void *data;
@@ -841,10 +841,8 @@ static void play_sfx(riscv_t *rv)
         .size = sfx_data_size,
         .volume = volume,
     };
-#if RV32_HAS(SDL_MIXER)
     pthread_create(&sfx_thread, NULL, sfx_handler, &sfx);
     sfx_thread_init = true;
-#endif
     /* FIXME: In web browser runtime, web workers in thread pool do not reap
      * after sfx_handler return, thus we have to join them. sfx_handler does not
      * contain infinite loop,so do not worry to be stalled by it */
@@ -900,10 +898,8 @@ static void play_music(riscv_t *rv)
         .looping = looping,
         .volume = volume,
     };
-#if RV32_HAS(SDL_MIXER)
     pthread_create(&music_thread, NULL, music_handler, &music);
     music_thread_init = true;
-#endif
     /* FIXME: In web browser runtime, web workers in thread pool do not reap
      * after music_handler return, thus we have to join them. music_handler does
      * not contain infinite loop,so do not worry to be stalled by it */
@@ -927,6 +923,7 @@ static void set_music_volume(riscv_t *rv)
 }
 #endif /* RV32_HAS(SDL_MIXER) */
 
+#if RV32_HAS(SDL_MIXER)
 static void init_audio(void)
 {
     if (!(SDL_WasInit(-1) & SDL_INIT_AUDIO)) {
@@ -943,7 +940,6 @@ static void init_audio(void)
         exit(EXIT_FAILURE);
     }
 
-#if RV32_HAS(SDL_MIXER)
     /* Initialize SDL2 Mixer */
     if (Mix_Init(MIX_INIT_MID) != MIX_INIT_MID) {
         rv_log_fatal("Mix_Init failed: %s", Mix_GetError());
@@ -954,10 +950,11 @@ static void init_audio(void)
         Mix_Quit();
         exit(EXIT_FAILURE);
     }
-#endif
     audio_init = true;
 }
+#endif
 
+#if RV32_HAS(SDL_MIXER)
 static void shutdown_audio()
 {
     /*
@@ -968,7 +965,6 @@ static void shutdown_audio()
      * on a valid pthread_t identifier.
      */
 
-#if RV32_HAS(SDL_MIXER)
     if (music_thread_init) {
         stop_music();
         pthread_join(music_thread, NULL);
@@ -987,10 +983,10 @@ static void shutdown_audio()
 
     Mix_CloseAudio();
     Mix_Quit();
-#endif
 
     audio_init = sfx_thread_init = music_thread_init = false;
 }
+#endif
 
 void sdl_video_audio_cleanup()
 {
@@ -998,6 +994,8 @@ void sdl_video_audio_cleanup()
         SDL_DestroyWindow(window);
         window = NULL;
     }
+
+#if RV32_HAS(SDL_MIXER)
     /*
      * The sfx_or_music_thread_init flag might not be set if a quick ctrl-c
      * occurs while the audio configuration is being initialized. Therefore,
@@ -1006,6 +1004,7 @@ void sdl_video_audio_cleanup()
     bool sfx_or_music_thread_init = sfx_thread_init | music_thread_init;
     if (sfx_or_music_thread_init || (!sfx_or_music_thread_init && audio_init))
         shutdown_audio();
+#endif
     SDL_Quit();
 }
 
@@ -1016,10 +1015,14 @@ void syscall_setup_audio(riscv_t *rv)
 
     switch (request) {
     case INIT_AUDIO:
+#if RV32_HAS(SDL_MIXER)
         init_audio();
+#endif
         break;
     case SHUTDOWN_AUDIO:
+#if RV32_HAS(SDL_MIXER)
         shutdown_audio();
+#endif
         break;
     default:
         rv_log_error("Unknown sound request: %d", request);