Implement change to cmake_ext_mod config folder

Tested: local linux

git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@25188 dab4d1a6-ed17-0410-a064-d1ae371a2980
Fix CMP0053 cmake usage

git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@25189 dab4d1a6-ed17-0410-a064-d1ae371a2980