Applied patch [ 606713 ] Removes a warning from cygwin build

Applied patch [ 606713 ] Removes a warning from cygwin build

When building using Cygwin+gcc3.1.1 I get the following
warning:

"src/msw/app.cpp:122:25: warning: shlwapi.h: No such
file or directory"

(It seems strange to me that it's a warning instead of an
error?)

The attached patch adds a conditional case for
__CYGWIN__ when including shlwapi.h. (I hope I did it
the proper way, the #if's regarding build system setup
get a bit lengthy at times, I didn't see a shortcut for this
however)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@17113 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775