build: Use __CYGWIN__ to detect Cygwin

The old __CYGWIN32__ does not work with the 64-bit version
of Cygiwn. Using __CYGWIN__ instead allows us to build
gen_idt.c under 64-bit Cygwin.

Change-Id: I6590767153e929764f0b448f74bb8e3f2e593a6a
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
1 file changed