Fixed the calculation of sy_nargs in sysent tables. We attempted to do
this in awk using the hack of counting args of type off_t twice and args
of all other types once. This is too simple to work. It gave benignly
wrong results on alphas (off_t shouldn't be counted twice) and for
svr4_sys_mmap64() on i386's (off64_t should be counted twice). It gave
fatally wrong results for i386's with 64-bit longs (longs should be
counted twice). The correct value for sy_nargs is easier to determine
from the size of the args struct anyway, except for complications to
make the generated code almost readable.

Improved formatting of sysent tables by lining up the comments where
possible.