patch for COFF .section

[Mark E.]

Thanks for checking it in.

I've studied the !BFD_ASSEMBLER version of obj_coff_section and it also 
doesn't warn in not warning about changing attributes after they've already 
been set, but with a twist. !bfd gas for DJGPP takes this:
.section .foo,"x"
.section .foo,"b"
.section .foo,"w"

and sets the section attributes for code, data, and bss.

The problem with fixing this is you can't tell the difference between a 
section that was just created by subseg_new and an existing section that 
happens to have the default flags.

Mark