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/rand.cpp

@@ -54,7 +54,7 @@ template<typename Scalar> void check_histogram(Scalar x, Scalar y, int bins)
   VERIFY( (((hist.cast<double>()/double(f))-1.0).abs()<0.02).all() );
 }
 
-void test_rand()
+EIGEN_DECLARE_TEST(rand)
 {
   long long_ref = NumTraits<long>::highest()/10;
   signed char char_offset = (std::min)(g_repeat,64);