test-suite: apply cleanup pass

Remove all non-modifiable items (target tuple, gcc version, toolchain path...)
Makefile syntax ( use $(...) instead of ${...} )
Update doc
Space-damage cleanups

 # Compute Alpha-specific values

 CT_DoArchTupleValues () {

     # The architecture part of the tuple:

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

 }