Prevent g++ warning for the ignored pragma.

src/error.hpp

@@ -39,10 +39,6 @@
 #include <string>
 #include <iosfwd>
 
-// Disable warnings "non - DLL-interface classkey 'identifier' used as base
-// for DLL-interface classkey 'identifier'"
-#pragma warning( disable : 4275 )
-
 // *****************************************************************************
 // namespace extensions
 namespace Exiv2 {
@@ -50,6 +46,12 @@ namespace Exiv2 {
 // *****************************************************************************
 // class definitions
 
+#ifdef _MSC_VER
+// Disable MSVC warnings "non - DLL-interface classkey 'identifier' used as base
+// for DLL-interface classkey 'identifier'"
+# pragma warning( disable : 4275 )
+#endif
+
     /*!
       @brief Error class interface. Allows the definition and use of a hierarchy
              of error classes which can all be handled in one catch block.
@@ -151,9 +153,9 @@ namespace Exiv2 {
 
     }; // class Error
 
-}                                       // namespace Exiv2
-
-// non - DLL-interface classkey 'identifier' used as base for DLL-interface classkey 'identifier'
-#pragma warning( default : 4275 )
+#ifdef _MSC_VER
+# pragma warning( default : 4275 )
+#endif
 
+}                                       // namespace Exiv2
 #endif                                  // #ifndef ERROR_HPP_