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 AVR32-specific values

 CT_DoArchTupleValues() {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}"

     # gcc ./configure flags

     CT_ARCH_WITH_ARCH=

     CT_ARCH_WITH_ABI=

     CT_ARCH_WITH_CPU=

     CT_ARCH_WITH_TUNE=

     CT_ARCH_WITH_FPU=

     CT_ARCH_WITH_FLOAT=

     CT_TARGET_SYS=none

 }