fuzzers: disallow include command in more principal way

We should never allow include command for fuzzers and it can be
triggered also by direct set property.

fuzzers/fuzzer_load.c

@@ -28,11 +28,6 @@
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
-#if defined(MPV_LOAD_CONFIG_FILE) || defined(MPV_LOAD_INPUT_CONF)
-    if (memmem(data, size, "include", sizeof("include") - 1))
-        return 0;
-#endif
-
     // fmemopen doesn't have associated file descriptor, so we do copy.
     int fd = memfd_create("fuzz_mpv_load", 0);
     if (fd == -1)

meson.build

@@ -381,6 +381,7 @@ if get_option('fuzzers')
     endif
     # Adding flags manually until https://github.com/mesonbuild/meson/pull/9825
     flags += ['-fsanitize=address,undefined,fuzzer', '-fno-omit-frame-pointer']
+    flags += ['-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION']
     link_flags += ['-fsanitize=address,undefined,fuzzer', '-fno-omit-frame-pointer']
 endif
 

player/main.c

@@ -227,6 +227,9 @@ static bool handle_help_options(struct MPContext *mpctx)
 
 static int cfg_include(void *ctx, char *filename, int flags)
 {
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    return 1;
+#endif
     struct MPContext *mpctx = ctx;
     char *fname = mp_get_user_path(NULL, mpctx->global, filename);
     int r = m_config_parse_config_file(mpctx->mconfig, mpctx->global, fname, NULL, flags);