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/matrix_exponential.cpp

@@ -119,7 +119,7 @@ void randomTest(const MatrixType& m, double tol)
   }
 }
 
-void test_matrix_exponential()
+EIGEN_DECLARE_TEST(matrix_exponential)
 {
   CALL_SUBTEST_2(test2dRotation<double>(1e-13));
   CALL_SUBTEST_1(test2dRotation<float>(2e-5));  // was 1e-5, relaxed for clang 2.8 / linux / x86-64