put the proxy definition to Liferay-SDK/build-common-ivy.xml
e.g. there:
<if>
<not>
<available file="${ivy.home}/ivy-${ivy.version}.jar" />
</not>
<then>
<mkdir dir="${ivy.home}" />
<setproxy proxyhost="PROXY_SERVER_XX.XX..." proxyport="e.g.8080" proxyUser="USER-if-not-annonym" proxyPassword="USER-password-if-necessary"/>
<get
dest="${ivy.home}"
src="${ivy.jar.url}"
/>
</then>
</if>