gdb: use separate patches for upstream and ARC gdb

With bump of upstream GDB from 7.9 to 7.10 at least
100-no_extern_inline.patch became incompatible with
ARC gdb (which is still based on upstream 7.9 branch).

So until ARC support is not completely upstreamed
(which we expect to happen in coming months) we'll need to have
separate patches for ARC gdb.

This time clean build-tested for Netgear WNDRMAC & AXS101.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Cc: John Crispin <blogic@openwrt.org>
Cc: Jonas Gorski <jogo@openwrt.org>

SVN-Revision: 47491