use lowercase winbase.h for Windows (#520)

racket/src/ChezScheme/LOG

@@ -2118,3 +2118,11 @@
     x86.ss
 - add special case in cpnanopass.ss for (eq? (ftype-pointer-address x) 0)
     cpnanopass.ss
+- added missing #ifndef WIN32
+    gcwrapper.c
+- added initialization of __to_g to make gcc 7.5.0 happy
+    gc.c
+- updated Windows makefiles
+    c/Makefile.*nt
+- use lowercase for Windows include files
+    segment.c, windows.c

racket/src/ChezScheme/c/segment.c

@@ -106,7 +106,7 @@ void S_freemem(void *addr, iptr bytes) {
 #endif
 
 #if defined(USE_VIRTUAL_ALLOC)
-#include <WinBase.h>
+#include <winbase.h>
 void *S_getmem(iptr bytes, IBOOL zerofill, IBOOL for_code) {
   void *addr;
 

racket/src/ChezScheme/c/windows.c

@@ -307,7 +307,7 @@ int S_windows_open_exclusive(char *who, char *path, int flags) {
 }
 #endif
 
-#include <Winbase.h>
+#include <winbase.h>
 
 /* primitive version of flock compatible with Windows 95/98/ME.  A better
    version could be implemented for Windows NT/2000/XP using LockFileEx. */