Guard a winsock2.h include under the usual pragmas.

We missed this one. Microsoft doesn't usually pass their own level 4
warnings. Kenny Root reports this otherwise trips warnings on some
version of the Windows SDK.

Change-Id: I71dc837ff8ee52321483d26c3a2cd8676393d999
Reviewed-on: https://boringssl-review.googlesource.com/13110
Reviewed-by: Kenny Root <kroot@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/tool/client.cc b/tool/client.cc
index dd3f846..c832ab5 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -19,7 +19,9 @@
 #if !defined(OPENSSL_WINDOWS)
 #include <sys/select.h>
 #else
+OPENSSL_MSVC_PRAGMA(warning(push, 3))
 #include <winsock2.h>
+OPENSSL_MSVC_PRAGMA(warning(pop))
 #endif
 
 #include <openssl/err.h>