Build fix for Microsoft Visual C++

When ACTIVE_SET_CPP_DEBUG is defined, the #warning preprocessor is used which
is not supported by Microsoft Visual C++.


Former-commit-id: a5227078f04ee1cfb9f9b500029ae75357f914f2

include/igl/active_set.cpp

@@ -45,7 +45,7 @@ IGL_INLINE igl::SolverStatus igl::active_set(
   )
 {
 //#define ACTIVE_SET_CPP_DEBUG
-#ifdef ACTIVE_SET_CPP_DEBUG
+#if defined(ACTIVE_SET_CPP_DEBUG) && !defined(_MSC_VER)
 #  warning "ACTIVE_SET_CPP_DEBUG"
 #endif
   using namespace Eigen;