build: explicitly opt-in to new fixup_chains functionality for darwin

This replaces (but does not collide with) the previous bind_on_load. There
is technically no need to opt-in to this functionality as long as >= MacOS 11.0
is being targetted, but it will be helpful to see in the logs.

configure.ac

@@ -1008,6 +1008,7 @@ if test "$TARGET_OS" = "darwin"; then
   AX_CHECK_LINK_FLAG([-Wl,-dead_strip], [CORE_LDFLAGS="$CORE_LDFLAGS -Wl,-dead_strip"], [], [$LDFLAG_WERROR])
   AX_CHECK_LINK_FLAG([-Wl,-dead_strip_dylibs], [CORE_LDFLAGS="$CORE_LDFLAGS -Wl,-dead_strip_dylibs"], [], [$LDFLAG_WERROR])
   AX_CHECK_LINK_FLAG([-Wl,-bind_at_load], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-bind_at_load"], [], [$LDFLAG_WERROR])
+  AX_CHECK_LINK_FLAG([-Wl,-fixup_chains], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-fixup_chains"], [], [$LDFLAG_WERROR])
 fi
 
 AC_CHECK_HEADERS([endian.h sys/endian.h byteswap.h sys/select.h sys/prctl.h sys/sysctl.h vm/vm_param.h sys/vmmeter.h sys/resources.h])