Merge pull request #10800 from kpayson64/fix_alpine

Fix alpine build

src/core/lib/channel/channel_args.c

@@ -31,6 +31,8 @@
  *
  */
 
+#include <grpc/support/port_platform.h>
+
 #include <limits.h>
 #include <string.h>
 

tools/dockerfile/test/cxx_alpine_x64/Dockerfile

@@ -27,7 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-FROM alpine:3.3
+FROM alpine:3.5
 
 # Install Git and basic packages.
 RUN apk update && apk add \