cc/gcc: fix 128-bit long doubles option

Spotted by Arnaud LACOMBE:
http://sourceware.org/ml/crossgcc/2010-10/msg00122.html

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}"

}