wepoll: use lower-cased windows headers This matches their use throughout the rest of the project, and fixes the build when you are cross-compiling on Linux using mingw-w64. i.e: CC epoll.lo CC wepoll.lo CC signal.lo wepoll.c:138:10: fatal error: WS2tcpip.h: No such file or directory #include <WS2tcpip.h> ^~~~~~~~~~~~ compilation terminated. make[2]: *** [Makefile:1918: wepoll.lo] Error 1