[libFuzzer] Make msan.test:SimpleCmpTest succeed with less trials.

[dokyungs]

Summary

Currently SimpleCmpTest passes after 9,831,994 trials on x86_64/Linux
when the number of given trials is 10,000,000, just a little bigger than
that. This patch modifies SimpleCmpTest.cpp so that the test passes with less
trials, reducing its chances of future failures as libFuzzer evolves. More
specifically, this patch changes a 32-bit equality check to a 8-bit equality
check, making this test pass at 4,635,303 trials.

[morehouse]

LGTM

compiler-rt/test/fuzzer/SimpleCmpTest.cpp

 bool PrintOnce(int Line) {
   if (!AllLines[Line])
     fprintf(stderr, "Seen line %d\n", Line);
   AllLines[Line] = 1;
   return true;
 }
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
-  if (Size != 24) return 0;
+  if (Size != 21)
+    return 0;
   uint64_t x = 0;
   int64_t  y = 0;
   int32_t z = 0;
-  uint32_t a = 0;
+  uint8_t a = 0;
   memcpy(&x, Data, 8);  // 8
   memcpy(&y, Data + 8, 8);  // 16
   memcpy(&z, Data + 16, sizeof(z));  // 20
-  memcpy(&a, Data + 20, sizeof(a));  // 24
+  memcpy(&a, Data + 20, sizeof(a));  // 21
   const bool k32bit = sizeof(void*) == 4;
 
   if ((k32bit || x > 1234567890) && PrintOnce(__LINE__) &&
       (k32bit || x < 1234567895) && PrintOnce(__LINE__) &&
-      a == 0x4242 && PrintOnce(__LINE__) &&
+      a == 0x42 && PrintOnce(__LINE__) &&
       (k32bit || y >= 987654321) && PrintOnce(__LINE__) &&
       (k32bit || y <= 987654325) && PrintOnce(__LINE__) &&
       z < -10000 && PrintOnce(__LINE__) &&
       z >= -10005 && PrintOnce(__LINE__) &&
       z != -10003 && PrintOnce(__LINE__) &&
       true) {
     fprintf(stderr, "BINGO; Found the target: size %zd (%zd, %zd, %d, %d), exiting.\n",
             Size, x, y, z, a);
     exit(1);
   }
   return 0;
 }
 
 int AllLines[__LINE__ + 1];  // Must be the last line.