Emit error when qr() called with permutation output and CXSparse libr…

…ary is used (bug #66511)

* qr.cc (Fqr): Change BIST test of 'p' vector orientation to only run if SPQR
library is used.

* sparse-qr.cc (E): Use "#elif defined (HAVE_CXSPARSE)" compiler conditional
to detect use of CXSParse library and emit an error.

libinterp/corefcn/qr.cc

@@ -811,7 +811,7 @@ orthogonal basis of @code{span (A)}.
 %! [q, r, p] = qr (eye (3), 0);
 %! assert (size (p), [1, 3]);
 
-%!testif ; (__have_feature__ ("SPQR") && __have_feature__ ("CHOLMOD")) || __have_feature__ ("CXSPARSE") <*66488>
+%!testif ; (__have_feature__ ("SPQR") && __have_feature__ ("CHOLMOD")) <*66488>
 %! ## Orientation of 'p' output for sparse matrices
 %! [q, r, p] = qr (speye (3));
 %! assert (size (p), [3, 3]);

liboctave/numeric/sparse-qr.cc

@@ -215,6 +215,12 @@ sparse_qr<SPARSE_T>::sparse_qr_rep::E () const
       ret(i) = i + 1;
 
   return ret;
+#elif defined (HAVE_CXSPARSE)
+
+  (*current_liboctave_error_handler)
+    ("sparse-qr: permutation output is not supported by CXSparse");
+
+  return ColumnVector ();  // needed to suppress compiler warning
 
 #else