nmake.opt: add WITH_PDB=1 option to optionaly generate .pdb file on Release builds (patch by tolon, #5420)

git-svn-id: https://svn.osgeo.org/gdal/trunk@27143 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx