macros: add BSON_GNUC_CHECK_VERSION() macros.
macros: add BSON_GNUC_CHECK_VERSION() macros.

These should vastly cleanup some version checks throughout the codebase.

rayyang2000/libbson,Machyne/libbson,paulmelnikow/libbson,bjori/libbson,jqk6/libbson,jqk6/libbson,paulmelnikow/libbson,mongodb/libbson,4Second2None/libbson_tmp,rayyang2000/libbson,rayyang2000/libbson,mapr/libbson,ajdavis/libbson,derickr/libbson,remicollet/libbson,rcsanchez97/libbson,mapr/libbson,remicollet/libbson,mapr/libbson,remicollet/libbson,jqk6/libbson,derickr/libbson,Convey-Compliance/libbson,remicollet/libbson,alexeyvo/libbson,ksuarz/libbson,derickr/libbson,jqk6/libbson,rayyang2000/libbson,paulmelnikow/libbson,4Second2None/libbson_tmp,derickr/libbson,Convey-Compliance/libbson,rcsanchez97/libbson,bjori/libbson,paulmelnikow/libbson,4Second2None/libbson_tmp,ajdavis/libbson,mongodb/libbson,ksuarz/libbson,paulmelnikow/libbson,4Second2None/libbson_tmp,Machyne/libbson,mongodbinc-interns/libbson,mongodbinc-interns/libbson,mongodbinc-interns/libbson,alexeyvo/libbson,Machyne/libbson,Machyne/libbson,ajdavis/libbson,alexeyvo/libbson,Convey-Compliance/libbson,ksuarz/libbson,rcsanchez97/libbson,mongodbinc-interns/libbson,bjori/libbson,mongodb/libbson