[MLIR] Add missing APSInt.h include

Since fd7e309 this is no longer
pulled in indirectly through DenseMapInfo.h.

mlir/lib/IR/BuiltinAttributes.cpp

@@ -15,6 +15,7 @@
 #include "mlir/IR/IntegerSet.h"
 #include "mlir/IR/Types.h"
 #include "mlir/Interfaces/DecodeAttributesInterfaces.h"
+#include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Endian.h"