IMPALA-4650: Allow protobuf to find non-system libraries and binaries
IMPALA-4650: Allow protobuf to find non-system libraries and binaries

This change makes PROTOBUF_GENERATE_CPP able to pick up Protobuf
libraries and binaries that are found by CMake but not installed on the
system LD_LIBRARY_PATH.

Change-Id: I942b3f18e25e2abc5aac167412b65abb680d3c5a
Reviewed-on: http://gerrit.cloudera.org:8080/5658
Tested-by: Impala Public Jenkins
Reviewed-by: Henry Robinson <3eca10f30041813f045165784e24b5a950a6cc7e@cloudera.com>

michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala