CDRIVER-2402 compile bundled libbson
CDRIVER-2402 compile bundled libbson

If the current source directory is not the source directory (i.e mongoc
is a subproject), build mongoc and libbson dependency.

mongodb/mongo-c-driver,ajdavis/mongo-c-driver,jmikola/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,rcsanchez97/mongo-c-driver,ajdavis/mongo-c-driver,acmorrow/mongo-c-driver,beingmeta/mongo-c-driver,beingmeta/mongo-c-driver,derickr/mongo-c-driver,ajdavis/mongo-c-driver,remicollet/mongo-c-driver,jmikola/mongo-c-driver,beingmeta/mongo-c-driver,ajdavis/mongo-c-driver,rcsanchez97/mongo-c-driver,acmorrow/mongo-c-driver,mongodb/mongo-c-driver,remicollet/mongo-c-driver,mongodb/mongo-c-driver,beingmeta/mongo-c-driver,ajdavis/mongo-c-driver,derickr/mongo-c-driver,remicollet/mongo-c-driver,jmikola/mongo-c-driver,mongodb/mongo-c-driver,jmikola/mongo-c-driver,acmorrow/mongo-c-driver,rcsanchez97/mongo-c-driver,derickr/mongo-c-driver,rcsanchez97/mongo-c-driver,derickr/mongo-c-driver,acmorrow/mongo-c-driver,derickr/mongo-c-driver,mongodb/mongo-c-driver,derickr/mongo-c-driver,remicollet/mongo-c-driver,jmikola/mongo-c-driver,beingmeta/mongo-c-driver,mongodb/mongo-c-driver,ajdavis/mongo-c-driver,remicollet/mongo-c-driver,rcsanchez97/mongo-c-driver,acmorrow/mongo-c-driver,rcsanchez97/mongo-c-driver,beingmeta/mongo-c-driver,acmorrow/mongo-c-driver,rcsanchez97/mongo-c-driver,jmikola/mongo-c-driver,jmikola/mongo-c-driver,remicollet/mongo-c-driver,remicollet/mongo-c-driver,ajdavis/mongo-c-driver,derickr/mongo-c-driver,beingmeta/mongo-c-driver,acmorrow/mongo-c-driver