mingw: Fix compilation issues

- use lowercase windows.h
- fix for mingw32 using preprocessor-unfriendly definition of CLOCKS_PER_SEC

unix/modtime.c

@@ -45,9 +45,19 @@ void msec_sleep_tv(struct timeval *tv) {
 #define sleep_select select
 #endif
 
-#if CLOCKS_PER_SEC == 1000000 // POSIX
+// mingw32 defines CLOCKS_PER_SEC as ((clock_t)<somevalue>) but preprocessor does not handle casts
+#if defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR)
+#define MP_REMOVE_BRACKETSA(x)
+#define MP_REMOVE_BRACKETSB(x) MP_REMOVE_BRACKETSA x
+#define MP_REMOVE_BRACKETSC(x) MP_REMOVE_BRACKETSB x
+#define MP_CLOCKS_PER_SEC MP_REMOVE_BRACKETSC(CLOCKS_PER_SEC)
+#else
+#define MP_CLOCKS_PER_SEC CLOCKS_PER_SEC
+#endif
+
+#if defined(MP_CLOCKS_PER_SEC) && (MP_CLOCKS_PER_SEC == 1000000) // POSIX
 #define CLOCK_DIV 1000.0
-#elif CLOCKS_PER_SEC == 1000 // WIN32
+#elif defined(MP_CLOCKS_PER_SEC) && (MP_CLOCKS_PER_SEC == 1000) // WIN32
 #define CLOCK_DIV 1.0
 #else
 #error Unsupported clock() implementation

windows/init.c

@@ -26,7 +26,7 @@
 
 #include <stdlib.h>
 #include <stdio.h>
-#include <Windows.h>
+#include <windows.h>
 
 HANDLE hSleepEvent = NULL;
 

windows/sleep.c

@@ -24,7 +24,7 @@
  * THE SOFTWARE.
  */
 
-#include <Windows.h>
+#include <windows.h>
 
 extern HANDLE hSleepEvent;