We now check to see if the destination .nasm file already exists. If
it does, then we don't try to convert the .asm to .nasm.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>