Improve bazel build for Windows.

Windows builds need some defines being set to use the static linking.

BUILD.bazel

@@ -1,3 +1,9 @@
+yaml_cpp_defines = select({
+    # On Windows, ensure static linking is used.
+    "@envoy//bazel:windows_x86_64": ["YAML_CPP_STATIC_DEFINE", "YAML_CPP_NO_CONTRIB"],
+    "//conditions:default": [],
+})
+
 cc_library(
     name = "yaml-cpp_internal",
     visibility = ["//:__subpackages__"],
@@ -11,4 +17,5 @@ cc_library(
     includes = ["include"],
     hdrs = glob(["include/**/*.h"]),
     srcs = glob(["src/**/*.cpp", "src/**/*.h"]),
+    defines = yaml_cpp_defines,
 )