This patch is required for QuRT. complex.h defines "I" and it replaces "I" in the 
enum definition without this patch creating an error.

diff --git a/Eigen/src/Core/SolveTriangular.h b/Eigen/src/Core/SolveTriangular.h
index ef17f28..1116270 100644
--- a/Eigen/src/Core/SolveTriangular.h
+++ b/Eigen/src/Core/SolveTriangular.h
@@ -112,6 +112,9 @@ template<typename Lhs, typename Rhs, int Mode, int Index, int Size,
          bool Stop = Index==Size>
 struct triangular_solver_unroller;
 
+#ifdef __PX4_QURT
+#undef I
+#endif
 template<typename Lhs, typename Rhs, int Mode, int Index, int Size>
 struct triangular_solver_unroller<Lhs,Rhs,Mode,Index,Size,false> {
   enum {