Only load .exe suffix'd completions on Cygwin.
Only load .exe suffix'd completions on Cygwin.

The only platform which actually needs to define .exe suffixes as
part of its completion set is Cygwin.  So don't define them on any
other platform.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git