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

test/prec_inverse_4x4.cpp

@@ -68,7 +68,7 @@ template<typename MatrixType> void inverse_general_4x4(int repeat)
   }
 }
 
-void test_prec_inverse_4x4()
+EIGEN_DECLARE_TEST(prec_inverse_4x4)
 {
   CALL_SUBTEST_1((inverse_permutation_4x4<Matrix4f>()));
   CALL_SUBTEST_1(( inverse_general_4x4<Matrix4f>(200000 * g_repeat) ));