mk: fix linking with some linux toolchains

mk: fix linking with some linux toolchains

Ubuntu/Debian toolchain passes --as-needed flag to the linker by default.
Add --no-as-needed flag by default in linuxapp exec-env to ensure correct
linking.

The problem arises because librte_eal doesn't add a DT_NEEDED entry for
librte_mempool despite the fact that it references symbols in that library.
It does this because we don't explicitly link with -lrte_mempool when we
build librte_eal.

Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>