CDRIVER-633 fix MinGW-W64 undefined symbols
CDRIVER-633 fix MinGW-W64 undefined symbols

RTL_RUN_ONCE and suseconds_t were undefined when building with CMake and
MinGW-W64. We conditionally define those if build with MS Visual Studio,
but we should conditionally define them if building on MS Windows, no
matter which compiler.

rcsanchez97/libbson,mapr/libbson,paulmelnikow/libbson,mongodb/libbson,bjori/libbson,paulmelnikow/libbson,mapr/libbson,bjori/libbson,paulmelnikow/libbson,mapr/libbson,mongodb/libbson,ajdavis/libbson,rcsanchez97/libbson,bjori/libbson,rcsanchez97/libbson,paulmelnikow/libbson,ajdavis/libbson,mongodb/libbson,paulmelnikow/libbson,ajdavis/libbson