GCC has -mrtd but the args are pushed in reverse versus PASCAL. So asm
routines have to use macros to obtain the stack arguments.
For the complex call_nls assembly, revert the arguments in C using a
preprocessor macro.
Because ia16-elf-gcc and the GNU linker do not understand OMF we
need to use ELF everywhere.
This also means we cannot use "wrt", "seg" and "call/jmp far".
Most wrt's are superfluous, and seg and call/jmp far can be
replaced by explicit ?GROUP references (to be defined in the
linker script).
