Fix use-after-move in test_parse_function_compiles and refactor
Fix use-after-move in test_parse_function_compiles and refactor

My recent patch had introduced a conditional use-after-move bug into the
test_parse_function_compiles function.  This patch fixes that by
reworking the entire test case into a compile-time check.  In my
opinion, we're not loosing anything by not actually executing the code
(the result wasn't looked at anyway) and the code becomes much clearer
by omitting the argument-preparation fluff.

ToruNiina/toml11