libc/uClibc: remove use of snapshots and specific date

We now have the ability to use a custom location, so supporting
snapshots or custom date is no longer needed. Let the user do the
required preparation in this case.

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

 # Compute Alpha-specific values

 CT_DoArchTupleValues () {

     # The architecture part of the tuple:

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

 }