[scudo] Delay allocations in the RSS check test

[cryptoad]

Summary

D57116 fails on the armv7 bots, which is I assume due to the timing of
the RSS check on the platform. While I don't have a platform to test
that change on, I assume this would do.

The test could be made more reliable by either delaying more the
allocations, or allocating more large-chunks, but both those options
have a somewhat non negligible impact (more memory used, longer test).

Hence me trying to keep the additional sleeping/allocating to a
minimum.

[yroux]

looks good to me, I'll keep an eye on the bots to check the fix. Thanks

test/scudo/rss.c

 static const size_t kNumAllocs = 64;
 static const size_t kAllocSize = 1 << 20;  // 1MB.
 
 static void *allocs[kNumAllocs];
 
 int main(int argc, char *argv[]) {
   int returned_null = 0;
   for (int i = 0; i < kNumAllocs; i++) {
-    if ((i & 0xf) == 0)
+    // sleep for 100ms every 8 allocations, to allow the RSS check to catch up.
+    if (i != 0 && (i & 0x7) == 0)
       usleep(100000);
     allocs[i] = malloc(kAllocSize);
     if (allocs[i])
       memset(allocs[i], 0xff, kAllocSize);  // Dirty the pages.
     else
       returned_null++;
   }
   for (int i = 0; i < kNumAllocs; i++)