Add missing declarations of explicit template instantiations. (#86591)

Found with `-Wundefined-func-template`.

Author: tkoeppe

mlir/include/mlir/Analysis/Presburger/Matrix.h

@@ -244,6 +244,9 @@ class Matrix {
   SmallVector<T, 16> data;
 };
 
+extern template class Matrix<MPInt>;
+extern template class Matrix<Fraction>;
+
 // An inherited class for integer matrices, with no new data attributes.
 // This is only used for the matrix-related methods which apply only
 // to integers (hermite normal form computation and row normalisation).