Fix compilation errors appearing due to missing <cstdint> include (#81233)

This patch resolves the issue by adding missing `<cstdint>` includes.
For SmallVector.h, such a change was already introduced in LLVM repository:
llvm/llvm-project@7e44305

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Author: kovdan01

include/swift/AST/FunctionRefInfo.h

@@ -21,6 +21,8 @@
 #include "swift/Basic/Debug.h"
 #include "swift/Basic/LLVM.h"
 
+#include <cstdint>
+
 namespace swift {
 
 class DeclNameLoc;

stdlib/include/llvm/ADT/SmallVector.h

@@ -21,6 +21,7 @@
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
+#include <cstdint>
 #include <cstdlib>
 #include <cstring>
 #include <functional>