atomic: cleanup GCC checks using new macros.
atomic: cleanup GCC checks using new macros.

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