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/mixingtypes.cpp

@@ -286,7 +286,7 @@ template<int SizeAtCompileType> void mixingtypes(int size = SizeAtCompileType)
   VERIFY_IS_APPROX( rcd.noalias() -= mcd + md*md,           - ((md*md).eval().template cast<CD>()) );
 }
 
-void test_mixingtypes()
+EIGEN_DECLARE_TEST(mixingtypes)
 {
   for(int i = 0; i < g_repeat; i++) {
     CALL_SUBTEST_1(mixingtypes<3>());