examples: select libgcc for non-default architecture

examples: select libgcc for non-default architecture

In case of multilib-enabled toolchains if default architecture differ from
the one examples are being built for linker will fail to link example object
files with libgcc of another (non-compatible) architecture.

Interesting enough for years in main Makefile we used CFLAGS/c_flags for this
but not for examples.

So fixing it now.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denx <wd@denx.de>
Acked-by: WOlfgang Denk <wd@denx.de>
Acked-by: Masahiro Yamada <yamada.m@jp.panasonic.com>