* coffread.c (decode_type): catch negative tagndx fields generated
by SCO 3.2v4 cc.
* exec.c: comment out string following #endif.
* configure.in (i[34]86-*-sco3.2v4*): use host i386sco4.
* xm-i386sco.h: include <sys/types.h> and <sys/dir.h>, required by
<sys/user.h>.
* config/i386sco4.mh: new file; like i386sco.mh, but don't require
gcc, and define const to empty to avoid SCO 3.2v4 cc bug.
