Simplify the format forwarding wrapper.
Simplify the format forwarding wrapper.

This passes all tests on MSC and seems to maybe address the problem on GCC as evidenced by this test case:
https://godbolt.org/g/aQHLxF
Note on that test that GCC generates what appears to be "wrong" code for `test` but correctly for `simplify` while
Clang generates the expected code for both functions. This definitely looks like the failure we're seeing on
Travis. I am still unclear why it works as expected locally, and also am unclear if this is a compiler bug or a bug
in formatxx, but in either case I think this is the fix. Hopefully.

seanmiddleditch/formatxx