-g with -native

[Matthew Fluet]

> Done.  Here's what the gcc calls now look like when compiling -g -native.
> 
> gcc -S -I/home/sweeks/mlton/include -g -w -fomit-frame-pointer -fno-strength-reduce -m486 -malign-loops=2 -malign-jumps=2 -malign-functions=2 -o /tmp/fileQuRrII.s /tmp/fileusayiD.c
> gcc -c -I/home/sweeks/mlton/include -g -w -fomit-frame-pointer -fno-strength-reduce -m486 -malign-loops=2 -malign-jumps=2 -malign-functions=2 -o /tmp/file0FnLUQ.o /tmp/fileQuRrII.s
> gcc -Wa --gstabs -c -I/home/sweeks/mlton/include -g -w -fomit-frame-pointer -fno-strength-reduce -m486 -malign-loops=2 -malign-jumps=2 -malign-functions=2 -o /tmp/filei1QNp0.o /tmp/fileXGq5SI.0.s
> gcc -I/home/sweeks/mlton/include -g -w -fomit-frame-pointer -fno-strength-reduce -m486 -malign-loops=2 -malign-jumps=2 -malign-functions=2 -o wrong /tmp/file0FnLUQ.o /tmp/filei1QNp0.o -L/home/sweeks/mlton/lib -lmlton-gdb -lm -lgmp

Looks good, but in the third call, "-Wa --gstabs" should be "-Wa,--gstabs"
(i.e., not two arguments, instead a single argument with a comma).  I
don't know what gcc does with the --gstabs option alone, but I don't get
an object file with line number debug info.