[fuzzer][test] Add #include <cstdint> for gcc-13

[tangyouling]

Summary

See https://gcc.gnu.org/gcc-13/porting_to.html#header-dep-changes.

[SixWeining]

Similar changes:
https://reviews.llvm.org/rG5e9be93566f39ee6cecd579401e453eccfbe81e5
https://reviews.llvm.org/rGff1681ddb303223973653f7f5f3f3435b48a1983
https://reviews.llvm.org/D137543

[xen0n]

Mentioned gcc-13 in the patch title and made the patch summary succinct by removing the error output and linking to the root justification of the change.

compiler-rt/test/fuzzer/CounterTest.cpp

 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 // Test for a fuzzer: must find the case where a particular basic block is
 // executed many times.
+#include <cstdint>
 #include <iostream>
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   int Num = 0;
   for (size_t i = 0; i < Size; i++)
     if (Data[i] == 'A' + i)
       Num++;
   if (Num >= 4) {
     std::cerr <<  "BINGO!\n";
     exit(1);
   }
   return 0;
 }

compiler-rt/test/fuzzer/FlagsTest.cpp

 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 // Parse some flags
+#include <cstdint>
 #include <string>
 #include <vector>
 
 static std::vector<std::string> Flags;
 
 extern "C" int LLVMFuzzerInitialize(int *Argc, char ***Argv) {
   // Parse --flags and anything after -ignore_remaining_args=1 is passed.
   int I = 1;