There is a problem in MicroEmacs 3.9e when compiled with the flags MSDOS
and MSC, under Microsoft-C. The DOS shell commands like ^X! do not work.
Looking in spawn.c and tracing down to execprog.c, there are 3 cases
selected by #if AZTEC #if LATTICE and #if TURBO in which the actual DOS
interrupts are done to create a child process and do the shell command.
There is no case for MSC!!!
This can be fixed by using the LATTICE case (change #if LATTICE to
#if LATTICE|MSC ) and by changing the error return line from
rval = -_oserr;
rval = -regs.x.ax;