werror: fix build in vcl

Change-Id: I30f9e1858c90943e1d369aeea02e10d8037a4ca8
diff --git a/vcl/source/opengl/OpenGLContext.cxx b/vcl/source/opengl/OpenGLContext.cxx
index 8253241..70a6cbc5 100644
--- a/vcl/source/opengl/OpenGLContext.cxx
+++ b/vcl/source/opengl/OpenGLContext.cxx
@@ -785,9 +785,13 @@ bool OpenGLContext::ImplInit()
            glXSwapInterval( 1 );

            if( errorTriggered )
            {
                SAL_WARN("vcl.opengl", "error when trying to set swap interval, NVIDIA or Mesa bug?");
            }
            else
            {
                VCL_GL_INFO("vcl.opengl", "set swap interval to 1 (enable vsync)");
            }
        }
    }

@@ -1359,6 +1363,7 @@ void OpenGLContext::makeCurrent()

    // move the context to the end of the contexts list
    static int nSwitch = 0;
    (void) nSwitch; // -Werror=unused-variable
    VCL_GL_INFO("vcl.opengl", "******* CONTEXT SWITCH " << ++nSwitch << " *********");
    if( mpNextContext )
    {