fix option order when invoking children

fix option order when invoking children

Poor getopt() implementations as found in many BSD/Darwin systems will
stop processing options after a non-option is encountered.  That means
ld-elf2flt has to be careful to not stick options after non-options when
executing sub children.  In a default setup, it will invoke `elf2flt` with
the output followed by the -a option which subsequently fails:
elf2flt: Can't open '-a': No such file or directory