toolchain: binutils: enhance build reproducability

built toolchain utilities will always operate in deterministic mode:
https://sourceware.org/binutils/docs-2.25/binutils/ar-cmdline.html



Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46137 3c298f89-4303-0410-b956-a3cf2f4a3e73