Odd warnings during build on Ubuntu 15.10

  CC       examples/bson_streaming_reader-bson-streaming-reader.o

  CCLD     libyajl.la

ar: `u' modifier ignored since `D' is the default (see `U')

  CCLD     libbson.la

ar: `u' modifier ignored since `D' is the default (see `U')

  CCLD     libbson-1.0.la

  CCLD     test-libbson

  CCLD     bson-to-json

  CCLD     bcon-speed

  CCLD     bson-validate

  CCLD     bcon-col-view

  CCLD     json-to-bson

  CCLD     bson-streaming-reader

  CCLD     bson-metrics