(gnulib): If have-cc-withh-libunwind is "yes", also mention -lunwind.

Makeconfig

@@ -511,7 +511,11 @@ link-libc-bounded = $(common-objpfx)libc_b.a $(gnulib) $(common-objpfx)libc_b.a
 link-extra-libs-bounded = $(foreach lib,$(LDLIBS-$(@F:%-bp=%)),$(common-objpfx)$(lib)_b.a)
 
 ifndef gnulib
-gnulib := -lgcc -lgcc_eh
+ifneq ($(have-cc-with-libunwind),yes)
+ gnulib := -lgcc -lgcc_eh
+else
+ gnulib := -lgcc -lgcc_eh -lunwind
+endif
 endif
 ifeq ($(elf),yes)
 +preinit = $(addprefix $(csu-objpfx),crti.o)