Ignore warnings from poly2tri

It's just UTF-8 in a comment!  clang -Wpedantic is too pedantic.

Author: roystgnr

src/mesh/poly2tri_triangulator.C

@@ -35,7 +35,9 @@
 #include "libmesh/utility.h"
 
 // poly2tri includes
+#include "libmesh/ignore_warnings.h" // utf-8 comments should be fine...
 #include "poly2tri/poly2tri.h"
+#include "libmesh/restore_warnings.h"
 
 // Anonymous namespace - poly2tri doesn't define operator<(Point,Point)
 namespace

tests/mesh/libmesh_poly2tri.C

@@ -2,7 +2,9 @@
 #include "libmesh_cppunit.h"
 
 #ifdef LIBMESH_HAVE_POLY2TRI
+#  include "libmesh/ignore_warnings.h" // utf-8 comments should be fine...
 #  include "poly2tri/poly2tri.h"
+#  include "libmesh/restore_warnings.h"
 #endif
 
 #include <numeric>