force cling compilation to be 32-bit when configuration is for a 32-bit arch (ROOT-5865).
force cling compilation to be 32-bit when configuration is for a 32-bit arch (ROOT-5865).

root-mirror/cling,root-mirror/cling,perovic/cling,root-mirror/cling,karies/cling,perovic/cling,root-mirror/cling,perovic/cling,marsupial/cling,root-mirror/cling,karies/cling,root-mirror/cling,marsupial/cling,karies/cling,karies/cling,marsupial/cling,marsupial/cling,karies/cling,marsupial/cling,perovic/cling,karies/cling,marsupial/cling,perovic/cling