libbsd: fix build for openrisc with uClibc

libbsd: fix build for openrisc with uClibc

Commit d879be30495 (package/libbsd: enable for non-glibc toolchains)
enabled libbsd for openrisc. Unfortunately uClibc does not define the
EM_OPENRISC macro that libbsd expects for ELF e_machine ID. Add patch
making libbsd fallback to the equivalent EM_OR1K macro that uClibc does
provide.

Fixes:
http://autobuild.buildroot.net/results/2f5/2f51eebe5964e8f1be3ecd2032e7d7837bf98b84/

Cc: Waldemar Brodkorb <wbx@openadk.org>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>