Enum element default arguments is a recent addition to the language.
With -enable-testing, default arguments can have public linkage.
Fixes <rdar://problem/53948283>.
Actually looking at the dumped IR is usually not interesting, the tests just
need to get to that stage to be able to perform the validation
correctly. Additionally, the IR is very large for some of these tests, so
dumping it makes things sllooooowww when something fails.