Fix compile warning in db_stress

Summary:
Fix compile warning in db_stress

Test Plan:
make db_stress

tools/db_stress.cc

@@ -28,6 +28,8 @@ int main() {
 }
 #else
 
+#define __STDC_FORMAT_MACROS
+#include <inttypes.h>
 #include <sys/types.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -1685,7 +1687,8 @@ class StressTest {
     fprintf(stdout, "Write percentage    : %d%%\n", FLAGS_writepercent);
     fprintf(stdout, "Delete percentage   : %d%%\n", FLAGS_delpercent);
     fprintf(stdout, "Iterate percentage  : %d%%\n", FLAGS_iterpercent);
-    fprintf(stdout, "DB-write-buffer-size: %llu\n", FLAGS_db_write_buffer_size);
+    fprintf(stdout, "DB-write-buffer-size: %" PRIu64 "\n",
+        FLAGS_db_write_buffer_size);
     fprintf(stdout, "Write-buffer-size   : %d\n", FLAGS_write_buffer_size);
     fprintf(stdout,
             "Iterations          : %lu\n",