debug/gdb: enforce gdbserver cross-compilation

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Message-Id: <ca85cad85c4dd20e74f1.1363446262@laptop>
Patchwork-Id: 228219

 # windows config options

 ## depends on ARCH_x86

 ##

 ## select WINDOWS

 ##

 ## help Build a toolchain targeting systems running Windows as host