debug/gdb: Fix compilation for Mingw hosts

GDB requires PDcurses instead of ncurses while running on Windows.
So, do not always compile ncurses in case GDB needs to build.

PDcurses is provided by an earlier build step and is not described in
this file.

Signed-off-by: Remy Bohmer <linux@bohmer.net>
[yann.morin.1998@anciense.nib.fr: we already have a way to detect ncurses usage]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Compute s390-specific values

CT_DoArchTupleValues() {

    # That's the only thing to override

    if [ "${CT_ARCH_64}" = "y" ]; then

        CT_TARGET_ARCH="s390x"

    fi

}