bpo-34217: Use lowercase for windows headers (GH-8472)

Modules/_io/_iomodule.c

@@ -21,7 +21,7 @@
 #endif /* HAVE_SYS_STAT_H */
 
 #ifdef MS_WINDOWS
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 /* Various interned strings */

Modules/socketmodule.c

@@ -303,7 +303,7 @@ http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/net/getaddrinfo.c.diff?r1=1.82&
 # endif
 
 /* Provides the IsWindows7SP1OrGreater() function */
-#include <VersionHelpers.h>
+#include <versionhelpers.h>
 
 /* remove some flags on older version Windows during run-time.
    https://msdn.microsoft.com/en-us/library/windows/desktop/ms738596.aspx */

Tools/msi/bundle/bootstrap/pch.h

@@ -15,7 +15,7 @@
 
 #include <windows.h>
 #include <gdiplus.h>
-#include <Uxtheme.h>
+#include <uxtheme.h>
 #include <msiquery.h>
 #include <objbase.h>
 #include <shlobj.h>