BUG#32045647: FIX WINDOWS C4251 COMPILER WARNINGS

Suppress benign MSVC C4251 warnings.
The warnings that are suppressed come from Google Protocol Buffers code.
According to the readme file at
https://github.com/protocolbuffers/protobuf/blob/master/cmake/README.md
these C4251 warnings can be disabled.

Change-Id: Id0bddd889d6c682edb198739610c28754d6fa5ac

Author: Daniel Blanchard

sql/immutable_string.h

@@ -45,6 +45,7 @@
 MY_COMPILER_DIAGNOSTIC_PUSH()
 MY_COMPILER_GCC_DIAGNOSTIC_IGNORE("-Wsuggest-override")
 MY_COMPILER_CLANG_DIAGNOSTIC_IGNORE("-Wdeprecated-dynamic-exception-spec")
+MY_COMPILER_MSVC_DIAGNOSTIC_IGNORE(4251)
 #include <google/protobuf/io/coded_stream.h>
 MY_COMPILER_DIAGNOSTIC_POP()