The valgrind configure script checks if host_cpu is set to armv7 or arm.
By default --host is set to arm-openwrt-linux and the host_cpu variable
is set to arm. Then the valgrind build tries to compile valgrind for
armv6 and fails. Set it explicitly to armv7 to compile valgrind with
armv7 support.
Fixes: 1a55d90320c1 ("valgrind: Update to version 3.23")
Link: https://github.com/openwrt/openwrt/pull/16633
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>