win: use lower case file names when importing Windows SDK headers

Although the header files included in the official Windows SDK have
mixed case file names, MinGW opted to ship headers with entirely lower
case names.

Since the MinGW headers are often used when cross compiling Windows
binaries on Linux hosts, and Linux treats paths as case sensitive by
default, following the 'official' spelling breaks many cross build
setups.

Non-cross builds do not seem to be affected by using lower case file
names, and Microsoft also does not seem particularly consistent in the
way it spells header file names in e.g. documentation and sample code.

Therefore, this patch makes wepoll use lower case file names when
including Windows headers, regardless of whether MinGW or the official
SDK is used.

See also https://github.com/libevent/libevent/pull/1039
and https://github.com/stjepang/smol/issues/138.

Closes: https://github.com/piscisaureus/wepoll/pull/19

src/win.h

@@ -1,34 +1,29 @@
 #ifndef WEPOLL_WIN_H_
 #define WEPOLL_WIN_H_
 
-#ifndef WIN32_LEAN_AND_MEAN
+#if defined(__clang__)
-#define WIN32_LEAN_AND_MEAN
-#endif
-
-#ifdef __clang__
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnonportable-system-include-path"
 #pragma clang diagnostic ignored "-Wreserved-id-macro"
-#endif
+#elif defined(_MSC_VER)
-
-#ifdef _WIN32_WINNT
-#undef _WIN32_WINNT
-#endif
-
-#define _WIN32_WINNT 0x0600
-
-#ifdef __clang__
-#pragma clang diagnostic pop
-#endif
-
-#ifndef __GNUC__
 #pragma warning(push, 1)
 #endif
 
-#include <WS2tcpip.h>
+#undef WIN32_LEAN_AND_MEAN
-#include <WinSock2.h>
+#define WIN32_LEAN_AND_MEAN
-#include <Windows.h>
 
-#ifndef __GNUC__
+#undef _WIN32_WINNT
+#define _WIN32_WINNT 0x0600
+
+/* clang-format off */
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#include <windows.h>
+/* clang-format on */
+
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#elif defined(_MSC_VER)
 #pragma warning(pop)
 #endif