Replace usage of _WIN32 in examples as this does not guarantee the
presence of wincodec.h.
mingw-w64 notably includes wincodec.h, though other releases do not.
Under cygwin the following can be used for a WIC enabled binary:
./configure --target=i686-pc-mingw32 CC=i686-w64-mingw32-gcc.exe
Change-Id: Ica6a714c3356a8eaf88486a1c3f5aa6adde394c0