[Bug c++/87381] clang 6.0 will compile this constexpr construct, but gcc 8.2.1 will not.

[eric-bugs at omnifarious dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87381

--- Comment #3 from eric-bugs at omnifarious dot org ---
Ahh, I guess that does make sense. Oh, well. I guess I'm stuck using template
arguments in place of function arguments in some cases.