Steffen Dettmer authored Aug 07, 2017 and Brad King committed Aug 30, 2017

Use `try_compile` instead of `try_run`.  It is not clear why `try_run`
was ever needed, and it does not work during cross-compiling.

Update the check's source file to remove code associated with actually
running things.  Also remove the ancient `__CLASSIC_C__` code path and
use a simple `int main(void)` as in `Modules/CheckIncludeFile.c.in`.

Fixes: #16920