Add static check indicating NT vs 9x/ME

This will be used/needed for some APIs that exist on both platforms but with different behavior/capabilities.

library/std/src/sys/windows/c/windows_sys.lst

@@ -2623,3 +2623,6 @@ Windows.Win32.System.Threading.GetCurrentThreadId
 Windows.Win32.Networking.WinSock.WSAPROTOCOL_INFOA
 Windows.Win32.Networking.WinSock.WSASocketA
 Windows.Win32.Networking.WinSock.WSADuplicateSocketA
+
+// NT vs 9x compat
+Windows.Win32.System.SystemInformation.GetVersion

library/std/src/sys/windows/c/windows_sys.rs

@@ -401,6 +401,10 @@ extern "system" {
     pub fn GetTickCount() -> u32;
 }
 #[link(name = "kernel32")]
+extern "system" {
+    pub fn GetVersion() -> u32;
+}
+#[link(name = "kernel32")]
 extern "system" {
     pub fn GetWindowsDirectoryW(lpbuffer: PWSTR, usize: u32) -> u32;
 }

library/std/src/sys/windows/compat.rs

@@ -24,6 +24,9 @@ use crate::ptr::NonNull;
 use crate::sync::atomic::Ordering;
 use crate::sys::c;
 
+mod version;
+pub use version::is_windows_nt;
+
 // This uses a static initializer to preload some imported functions.
 // The CRT (C runtime) executes static initializers before `main`
 // is called (for binaries) and before `DllMain` is called (for DLLs).
@@ -63,6 +66,8 @@ unsafe extern "C" fn init() {
     // because this function runs during global initialization. For example, DO NOT
     // do any dynamic allocation, don't call LoadLibrary, etc.
 
+    version::init_windows_version_check();
+
     // check all the different synchronization primitives ...
     load_try_enter_critical_section_function();
     load_srw_functions();

library/std/src/sys/windows/compat/version.rs

@@ -0,0 +1,15 @@
+use crate::sys::c;
+
+static mut IS_NT: bool = true;
+
+pub fn init_windows_version_check() {
+    // according to old MSDN info, the high-order bit is set only on 95/98/ME.
+    unsafe { IS_NT = c::GetVersion() < 0x8000_0000 };
+}
+
+/// Returns true if we are running on a Windows NT-based system. Only use this for APIs where the
+/// same API differs in behavior or capability on 9x/ME compared to NT.
+#[inline(always)]
+pub fn is_windows_nt() -> bool {
+    unsafe { IS_NT }
+}