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

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

Reviewed By: SixWeining

Differential Revision: https://reviews.llvm.org/D137696

compiler-rt/test/fuzzer/CounterTest.cpp

@@ -4,6 +4,7 @@
 
 // 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) {

compiler-rt/test/fuzzer/FlagsTest.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 // Parse some flags
+#include <cstdint>
 #include <string>
 #include <vector>