PR target/47098 OBSD_LIB_SPEC on i686-openbsd3 missing

PR target/47098 OBSD_LIB_SPEC on i686-openbsd3 missing

config-list.mk for i686-*-openbsd3.0 failed with:

gcc/config/openbsd.h:143:18: error: ‘OBSD_LIB_SPEC’ was not declared in this scope
 #define LIB_SPEC OBSD_LIB_SPEC
                  ^
gcc/gcc.c:879:31: note:
in expansion of macro ‘LIB_SPEC’
 static const char *lib_spec = LIB_SPEC;
                               ^
make[2]: *** [gcc.o] Error 1

i.e. openbsd-oldgas.h is only used on
i?86-*-openbsd2.*|i?86-*openbsd3.[0123] so add the OBSD_LIB_SPEC there

From-SVN: r222315