Fix Windows build.

When using CMake to build with MSVC, MSVC complains about unreachable
code in the <xtree> header. This incantation silences that.

Change-Id: I5fc5305dc816a009a4c59501b212fd11e290637d
Reviewed-on: https://boringssl-review.googlesource.com/5552
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

crypto/evp/evp_test.cc

@@ -56,10 +56,19 @@
 #include <stdlib.h>
 #include <string.h>
 
+#if defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable: 4702)
+#endif
+
 #include <map>
 #include <string>
 #include <vector>
 
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
+
 #include <openssl/bio.h>
 #include <openssl/crypto.h>
 #include <openssl/digest.h>

crypto/test/file_test.h

@@ -18,11 +18,19 @@
 #include <stdint.h>
 #include <stdio.h>
 
+#if defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable: 4702)
+#endif
+
 #include <string>
 #include <map>
 #include <set>
 #include <vector>
 
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
 
 // File-based test framework.
 //