UseJava.cmake: fully use cmake_parse_arguments in add_jar

Modify add_jar to fully use named arguments, rather than cmake
variables, for specifying output names/directories, etc. For backward
compatibility, the old variables are still honored if set, although
named arguments will override them.
FindProtobuf: also find pthread

Modify FindProtobuf.cmake to find the pthread library on UNIX platforms,
and to add the same to PROTOBUF_LIBRARIES, as this is a link dependency
of libraries using the protobuf headers.
Merge topic 'fix-protobuf-threads' into next

8961c4b FindProtobuf: also find pthread
Merge topic 'use-java-use-parse-arguments' into next

81b5fb5 UseJava.cmake: fully use cmake_parse_arguments in add_jar