cmake AWS_HAVE_MSVC_INTRINSICS_X64 examples

awslabs/aws-c-common cmake/AwsFeatureTests.cmake :123 

check_c_source_compiles("
    #include <intrin.h>
    int main() {
        unsigned __int64 a = 0x0fffffffffffffffI64;
        unsigned __int64 b = 0xf0000000I64;
        unsigned __int64 c, d;
        d = _umul128(a, b, &c);
        return 0;
    }" AWS_HAVE_MSVC_INTRINSICS_X64)