* coffcode.h (styp_to_sec_flags): If COFF_LONG_SECTION_NAMES and
COFF_SUPPORT_GNU_LINKONCE, mark sections whose names begin with
.gnu.linkonce with SEC_LINKONCE and SEC_LINK_DUPLICATES_DISCARD.
* coff-go32.c: (COFF_LONG_SECTION_NAMES): Define.
(COFF_SUPPORT_GNU_LINKONCE): Define.
* coff-stgo32.c: (COFF_LONG_SECTION_NAMES): Define.
(COFF_SUPPORT_GNU_LINKONCE): Define.