libunwind: don't use gold for mips

libunwind: don't use gold for mips

The gold doesn't work for mips or mips64:
configure:3867: checking whether the C compiler works
configure:3889: mips-poky-linux-gcc  -meb -mabi=32 -mhard-float -march=mips32r2 --sysroot=/buildarea/lyang1/test_uni/tmp/sysroots/qemumips  -O2 -pipe -g -feliminate-unused-debug-types   -Wl,-O1  -Wl,--as-needed  -fuse-ld=gold conftest.c  >&5
collect2: fatal error: cannot find 'ld'

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>