[Bug c++/89741] [9 Regression] static_assert fires when template not instantiated

[tadeus.prastowo at unitn dot it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89741

--- Comment #4 from Tadeus Prastowo <tadeus.prastowo at unitn dot it> ---
My use-case is to use the instantiation of `struct X' to fire the static
assert.