CDRIVER-1314 define va_copy in C89
CDRIVER-1314 define va_copy in C89

mapr/libbson,ajdavis/libbson,mapr/libbson,ajdavis/libbson,paulmelnikow/libbson,mongodb/libbson,paulmelnikow/libbson,Convey-Compliance/libbson,ajdavis/libbson,paulmelnikow/libbson,Convey-Compliance/libbson,rcsanchez97/libbson,rcsanchez97/libbson,mongodb/libbson,paulmelnikow/libbson,alexeyvo/libbson,alexeyvo/libbson,bjori/libbson,mapr/libbson,alexeyvo/libbson,Convey-Compliance/libbson,rcsanchez97/libbson,paulmelnikow/libbson,bjori/libbson,mongodb/libbson,bjori/libbson