build: ./configure basic cross-compilation support

build: ./configure basic cross-compilation support

$ sudo dpkg --add-architecture arm64
[update APT sources.list]
$ sudo apt install qemu crossbuild-essential-arm64 libssl-dev:arm64 libuuid1:arm64 libnl-3-dev:arm64 libnl-route-3-dev:arm64
$ ./configure -w -a aarch64
$ ninja
$ uname -m
x86_64
$ bin/vpp unix interactive
    _______    _        _   _____  ___
 __/ __/ _ \  (_)__    | | / / _ \/ _ \
 _/ _// // / / / _ \   | |/ / ___/ ___/
 /_/ /____(_)_/\___/   |___/_/  /_/

vpp# show cpu
Model name:               armv8
Microarch model (family): unknown (implementer 0x55 part 0x32c PASS 89.1519459600)
Flags:                    fp asimd aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm jscvt fcma lrcpc dcpop sha3 sm3 sm4 asimddp sha512 sve
Base frequency:           .06 GHz
vpp#

Type: make
Change-Id: Ib8bf2c7e38f109db42225db2e3182ceb8871baaf
Signed-off-by: Damjan Marion <damarion@cisco.com>