This was broken by the varargs changes in commit a20d69a211. The code was not accounting for the internal representation of the parameters being in reverse order, so it was basing address calculations on the first fixed parameter rather than the last one, resulting in the wrong number of bytes being removed from the stack (generally causing a crash).
This affected the c99stdio.c test case, and is now also covered in c99stdarg.c.
These are currently only run by the new DOIT3 test-running script.
Note that these tests are designed to be applicable to most implementations of C95/C99/C11, not just ORCA/C. They do make certain assumptions not guaranteed by the standards (e.g. power of 2 types and some properties of IEEE-like FP), but in general those assumptions should be true for most 'normal' systems.
These involve recent standards-conformance patches for printf and scanf, which changed some (non-standard) behaviors that the test cases were expecting.
I also fixed a couple things that clang flagged as undefined behavior, even though they weren't really causing problems under ORCA/C.
