POSIXify ./configure, and comment some parts of it.
Thanks to Martin GUY for pointing out that ./configure was not POSIXly correct.

/trunk/configure | 51 35 16 0 +++++++++++++++++++++++++++++++++++----------------
1 file changed, 35 insertions(+), 16 deletions(-)

# Compute x86_64-specific values

CT_DoArchValues() {

    # The architecture part of the tuple:

    CT_TARGET_ARCH="${CT_ARCH}"

}