unify and bump _WIN32_WINNT definition to Windows 8.1

Git for Windows doesn't support anything prior to Windows 8.1 since 2.47.0
and Git followed along with commits like ce6ccba (mingw: drop Windows
7-specific work-around, 2025-08-04).

There is no need to pretend to the compiler that we still support Windows
Vista, just to lock us out of easy access to newer APIs. There is also no
need to have conflicting and unused definitions claiming we support some
versions of Windows XP or even Windows NT 4.0.

Bump all definitions of _WIN32_WINNT to a realistic value of Windows 8.1.
This will also simplify code for a followup commit that will improve cpu
core detection on multi-socket systems.

Signed-off-by: Matthias Aßhauer <mha1993@live.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: rimrul

compat/mingw.c

@@ -2464,7 +2464,7 @@ int mingw_rename(const char *pold, const char *pnew)
 	if (supports_file_rename_info_ex) {
 		/*
 		 * Our minimum required Windows version is still set to Windows
-		 * Vista. We thus have to declare required infrastructure for
+		 * 8.1. We thus have to declare required infrastructure for
 		 * FileRenameInfoEx ourselves until we bump _WIN32_WINNT to
 		 * 0x0A00. Furthermore, we have to handle cases where the
 		 * FileRenameInfoEx call isn't supported yet.

compat/nedmalloc/malloc.c.h

@@ -500,7 +500,7 @@ MAX_RELEASE_CHECK_RATE   default: 4095 unless not HAVE_MMAP
 #ifdef WIN32
 #define WIN32_LEAN_AND_MEAN
 #ifndef _WIN32_WINNT
-#define _WIN32_WINNT 0x403
+#define _WIN32_WINNT 0x603
 #endif
 #include <windows.h>
 #define HAVE_MMAP 1

compat/poll/poll.c

@@ -20,7 +20,7 @@
 
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
-/* To bump the minimum Windows version to Windows Vista */
+/* To bump the minimum Windows version to Windows 8.1 */
 #include "git-compat-util.h"
 
 /* Tell gcc not to warn about the (nfd < 0) tests, below.  */
@@ -41,7 +41,7 @@
 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
 # define WIN32_NATIVE
 # if defined (_MSC_VER) && !defined(_WIN32_WINNT)
-#  define _WIN32_WINNT 0x0502
+#  define _WIN32_WINNT 0x0603
 # endif
 # include <winsock2.h>
 # include <windows.h>

compat/posix.h

@@ -76,7 +76,7 @@
 
 #if defined(WIN32) && !defined(__CYGWIN__) /* Both MinGW and MSVC */
 # if !defined(_WIN32_WINNT)
-#  define _WIN32_WINNT 0x0600
+#  define _WIN32_WINNT 0x0603
 # endif
 #define WIN32_LEAN_AND_MEAN  /* stops windows.h including winsock.h */
 #include <winsock2.h>

compat/win32/flush.c

@@ -6,7 +6,9 @@ int win32_fsync_no_flush(int fd)
 {
        IO_STATUS_BLOCK io_status;
 
+#ifndef FLUSH_FLAGS_FILE_DATA_ONLY
 #define FLUSH_FLAGS_FILE_DATA_ONLY 1
+#endif
 
        DECLARE_PROC_ADDR(ntdll.dll, NTSTATUS, NTAPI, NtFlushBuffersFileEx,
 			 HANDLE FileHandle, ULONG Flags, PVOID Parameters, ULONG ParameterSize,