These functions are defined only when ENABLE_CAIRO_CANVAS

Class X11SalGraphics are derived from class SalGraphics, which is
defined in vcl/inc/salgdi.hxx. So these override functions should be
defined in the same condition as the base class.

Change-Id: I5af0ee9c89c74e66b8f2dbd44890606fc5e41b14
Reviewed-on: https://gerrit.libreoffice.org/23373Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

vcl/inc/unx/salgdi.h

@@ -259,12 +259,15 @@ public:
                                         long nHeight, sal_uInt8 nTransparency ) override;
 
     virtual SystemGraphicsData      GetGraphicsData() const override;
+
+#if ENABLE_CAIRO_CANVAS
     virtual bool                    SupportsCairo() const override;
     virtual cairo::SurfaceSharedPtr CreateSurface(const cairo::CairoSurfaceSharedPtr& rSurface) const override;
     virtual cairo::SurfaceSharedPtr CreateSurface(const OutputDevice& rRefDevice, int x, int y, int width, int height) const override;
     virtual cairo::SurfaceSharedPtr CreateBitmapSurface(const OutputDevice& rRefDevice, const BitmapSystemData& rData, const Size& rSize) const override;
     virtual css::uno::Any           GetNativeSurfaceHandle(cairo::SurfaceSharedPtr& rSurface, const basegfx::B2ISize& rSize) const override;
     virtual SystemFontData          GetSysFontData( int nFallbackLevel ) const override;
+#endif
 
     bool TryRenderCachedNativeControl(ControlCacheKey& aControlCacheKey,
                                       int nX, int nY);