config: rename variables that are arrays

Make it explicit that a variable is an array bu the name of the variable.
It will be used later when .config gets munged to allow both multiple
arguments and arguments with spaces at the same time to be passed from the
configuration down to the build scripts.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Compute Alpha-specific values

 CT_DoArchTupleValues () {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}${CT_ARCH_ALPHA_VARIANT}"

 }