[compiler-rt] Include windows.h with the right capitalization

[mstorsjo]

Summary

This is an issue if cross-building for windows from a case sensitive
file system.

(Updated summary to repost it to the list, I forgot to add the list as subscriber when posted initially.)

[mstorsjo]

Ping - I missed to add llvm-commits initially when creating it, so it never got posted to the list.

[mstorsjo]

Abandoning this one, and creating a new one, with reviewers preselected, as suggested by Vedant Kumar.

lib/builtins/enable_execute_stack.c

 /* #include "config.h"
  * FIXME: CMake - include when cmake system is ready.
  * Remove #define HAVE_SYSCONF 1 line.
  */
 #define HAVE_SYSCONF 1
 
 #ifdef _WIN32
 #define WIN32_LEAN_AND_MEAN
-#include <Windows.h>
+#include <windows.h>
 #else
 #ifndef __APPLE__
 #include <unistd.h>
 #endif /* __APPLE__ */
 #endif /* _WIN32 */
 
 #if __LP64__
   #define TRAMPOLINE_SIZE 48