Revert #a09246191120: cc/gcc: fix C++ headers location

This was intended as a fix for g++ not finding its headers,
but it breaks in othe horrible ways. So just revert it.

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}"

}