[NFC] Include <cstdlib> and <cstdint> where necessary.

Our Bazel builds have become more strict about libc++
dependencies recently, so these are required to pick up
declarations of `malloc` and `uint32_t`, respectively.

Author: allevato

include/swift/Demangling/Demangle.h

@@ -27,6 +27,7 @@
 
 #include <cassert>
 #include <cstdint>
+#include <cstdlib>
 #include <functional>
 #include <memory>
 #include <string>

include/swift/Remote/MemoryReader.h

@@ -22,6 +22,7 @@
 #include "swift/SwiftRemoteMirror/MemoryReaderInterface.h"
 #include <optional>
 
+#include <cstdlib>
 #include <cstring>
 #include <functional>
 #include <memory>

stdlib/public/Concurrency/Debug.h

@@ -17,6 +17,8 @@
 #ifndef SWIFT_CONCURRENCY_DEBUG_H
 #define SWIFT_CONCURRENCY_DEBUG_H
 
+#include <cstdint>
+
 #include "swift/Runtime/Config.h"
 
 namespace swift {