Get rid of EIGEN_TEST_FUNC, unit tests must now be declared with EIGEN_DECLARE_TEST(mytest) { /* code */ }.

This provide several advantages:
- more flexibility in designing unit tests
- unit tests can be glued to speed up compilation
- unit tests are compiled with same predefined macros, which is a requirement for zapcc

unsupported/test/openglsupport.cpp

@@ -106,7 +106,7 @@ GLint createShader(const char* vtx, const char* frg)
   return prg_id;
 }
 
-void test_openglsupport()
+EIGEN_DECLARE_TEST(openglsupport)
 {
   int argc = 0;
   glutInit(&argc, 0);