see https://gitlab.com/flightgear/simgear/-/work_items/56
fix compile with >=sci-libs/gdal-3.10
see https://github.com/OSGeo/gdal/pull/10605.patch
--- a/simgear/scene/dem/SGDemTile_gdal.cxx
+++ b/simgear/scene/dem/SGDemTile_gdal.cxx
@@ -546,7 +546,7 @@ void SGDemTile::doWarp( int iSrc, char* pszSrcFile, GDALDatasetH hDstDS, char**
 
     if( bHaveNodata )
     {
-        if (CPLIsNan(dfReal))
+        if (std::isnan(dfReal))
             printf( "Using internal nodata values (e.g. nan) for image %s.\n",
                     pszSrcFile );
         else