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/NonLinearOptimization.cpp

@@ -1818,7 +1818,7 @@ void testNistEckerle4(void)
   VERIFY_IS_APPROX(x[2], 4.5154121844E+02);
 }
 
-void test_NonLinearOptimization()
+EIGEN_DECLARE_TEST(NonLinearOptimization)
 {
     // Tests using the examples provided by (c)minpack
     CALL_SUBTEST/*_1*/(testChkder());