java/apache-commons-httpclient: make backwards compatible with java 8

Dependency openoffice needs java 8. Without this patch openoffice fails
with:
bad class file: /usr/local/share/java/classes/commons-httpclient.jar(org/apache/commons/httpclient/HttpClient.class)

class file has wrong version 65.0, should be 52.0
Please remove or make sure it appears in the correct subdirectory of the classpath.

So make httpclient target java 8 for now.

While here I added encoding= to javac instead of the REINPLACE_CMD statement.

PR: 293317
Approved-by: Alex Dupre (maintainer)