The GNU "doschk" (in non-gnu/) utility can tell you what's legal and what isn't.
http://www.delorie.com/gnu/dl/ftp.gnu.org/non-gnu/doschk/doschk-1.1.tar.gz/doschk-1.1/doschk.c Note, however, that @files used by gcc *in djgpp* will *not* support comments, because @files in djgpp are parsed and expanded by the djgpp runtime itself, not passed to gcc. So breaking compatibility with djgpp's implementation means that @files given to gcc will act differently on djgpp than on other systems.
