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/FFTW.cpp

@@ -225,7 +225,7 @@ void test_return_by_value(int len)
     VERIFY( (in1-in).norm() < test_precision<float>() );
 }
 
-void test_FFTW()
+EIGEN_DECLARE_TEST(FFTW)
 {
   CALL_SUBTEST( test_return_by_value(32) );
   //CALL_SUBTEST( ( test_complex2d<float,4,8> () ) ); CALL_SUBTEST( ( test_complex2d<double,4,8> () ) );