Mapcache build error

[szekerest]

MapCache doesn't build with the most recent gdal master with the following error

source_gdal.obj : error LNK2019: unresolved external symbol MIN referenced in function CreateWarpedVRT

This is because the MIN macro has been used from cpl_port.h but that has been removed by this commit

OSGeo/gdal@1f41ebc

We need to use MAPCACHE_MIN instead.