Fix warning suppression in the json utility. (#2462)

Properly push and pop the warning configuration to avoid unintentional
side effects. The previous solution could overwrite command line options
and the inclusion of the header can change what warnings are enabled.

src/include/souffle/utility/json11.h

@@ -66,6 +66,7 @@
 #include <vector>
 
 #ifdef _MSC_VER
+#pragma warning(push)
 #pragma warning(disable : 4244)
 #if _MSC_VER <= 1800  // VS 2013
 #ifndef noexcept
@@ -1111,7 +1112,7 @@ inline std::vector<Json> parse_multi(const std::string& in, std::string::size_ty
 }
 
 #ifdef _MSC_VER
-#pragma warning(default : 4244)
+#pragma warning(pop)
 #endif  // _MSC_VER
 
 }  // namespace json11