Build and test on ARM64 CPU architecture (#1)

* Build and test on ARM64 CPU architecture

Add an extra TravisCI job that runs `ci_build.sh` on arm64/aarch64 CPU architecture

Author: martin-g

.travis.yml

@@ -142,7 +142,22 @@ matrix:
         packages:
         - abi-dumper
         - abi-compliance-checker
-    
+  - name: Linux ARM64
+    env: BUILD_TYPE=default CURVE=tweetnacl GSSAPI=enabled PGM=enabled NORM=enabled IPv6=ON TLS=enabled DRAFT=enabled
+    os: linux
+    dist: bionic
+    arch: arm64
+    addons:
+      apt:
+        sources:
+        - sourceline: 'deb http://download.opensuse.org/repositories/network:/messaging:/zeromq:/git-stable/xUbuntu_18.04/ ./'
+          key_url: 'http://download.opensuse.org/repositories/network:/messaging:/zeromq:/git-stable/xUbuntu_18.04/Release.key'
+        packages:
+          - zip
+          - libkrb5-dev
+          - libnorm-dev
+          - libpgm-dev
+          - libgnutls28-dev
 
 before_install:
 - if [ $TRAVIS_OS_NAME == "osx" -a $BUILD_TYPE == "android" ] ; then brew update; brew install binutils ; fi