util: disable cache if we have no build-id and timestamp is zero

Timestamp can be zero for example when Flatpak is used. In this
case just disable the cache rather then segfaulting when
incompatible cache items are loaded.

V2: actually return false when mtime is 0.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

src/amd/vulkan/radv_device.c

@@ -61,10 +61,6 @@ radv_get_build_id(void *ptr, struct mesa_sha1 *ctx)
 	} else
 #endif
 	if (disk_cache_get_function_timestamp(ptr, &timestamp)) {
-		if (!timestamp) {
-			fprintf(stderr, "radv: The provided filesystem timestamp for the cache is bogus!\n");
-		}
-
 		_mesa_sha1_update(ctx, &timestamp, sizeof(timestamp));
 	} else
 		return false;

src/util/disk_cache.h

@@ -26,6 +26,7 @@
 
 #ifdef HAVE_DLFCN_H
 #include <dlfcn.h>
+#include <stdio.h>
 #endif
 #include <assert.h>
 #include <stdint.h>
@@ -100,7 +101,15 @@ disk_cache_get_function_timestamp(void *ptr, uint32_t* timestamp)
    if (stat(info.dli_fname, &st)) {
       return false;
    }
+
+   if (!st.st_mtime) {
+      fprintf(stderr, "Mesa: The provided filesystem timestamp for the cache "
+              "is bogus! Disabling On-disk cache.\n");
+      return false;
+   }
+
    *timestamp = st.st_mtime;
+
    return true;
 }
 #endif