Add startup check indicating NT vs 9x/ME

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

Author: seritools

library/std/src/sys/pal/windows/c/bindings.txt

@@ -2495,6 +2495,7 @@ Windows.Win32.System.SystemInformation.GetSystemDirectoryW
 Windows.Win32.System.SystemInformation.GetSystemInfo
 Windows.Win32.System.SystemInformation.GetSystemTimeAsFileTime
 Windows.Win32.System.SystemInformation.GetSystemTimePreciseAsFileTime
+Windows.Win32.System.SystemInformation.GetVersion
 Windows.Win32.System.SystemInformation.GetWindowsDirectoryW
 Windows.Win32.System.SystemInformation.PROCESSOR_ARCHITECTURE
 Windows.Win32.System.SystemInformation.SYSTEM_INFO

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

@@ -61,6 +61,7 @@ windows_targets::link!("kernel32.dll" "system" fn GetSystemInfo(lpsysteminfo : *
 windows_targets::link!("kernel32.dll" "system" fn GetSystemTimeAsFileTime(lpsystemtimeasfiletime : *mut FILETIME));
 windows_targets::link!("kernel32.dll" "system" fn GetSystemTimePreciseAsFileTime(lpsystemtimeasfiletime : *mut FILETIME));
 windows_targets::link!("kernel32.dll" "system" fn GetTempPathW(nbufferlength : u32, lpbuffer : PWSTR) -> u32);
+windows_targets::link!("kernel32.dll" "system" fn GetVersion() -> u32);
 windows_targets::link!("kernel32.dll" "system" fn GetWindowsDirectoryW(lpbuffer : PWSTR, usize : u32) -> u32);
 windows_targets::link!("kernel32.dll" "system" fn InitOnceBeginInitialize(lpinitonce : *mut INIT_ONCE, dwflags : u32, fpending : *mut BOOL, lpcontext : *mut *mut core::ffi::c_void) -> BOOL);
 windows_targets::link!("kernel32.dll" "system" fn InitOnceComplete(lpinitonce : *mut INIT_ONCE, dwflags : u32, lpcontext : *const core::ffi::c_void) -> BOOL);

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

@@ -23,6 +23,9 @@ use crate::ffi::{CStr, c_void};
 use crate::ptr::NonNull;
 use crate::sys::c;
 
+#[cfg(target_vendor = "rust9x")]
+pub(crate) mod checks;
+
 // 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).

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

@@ -0,0 +1,33 @@
+use crate::sys::c;
+
+/// 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.
+#[allow(dead_code)]
+#[inline(always)]
+#[cfg(target_arch = "x86")]
+pub fn is_windows_nt() -> bool {
+    unsafe { IS_NT }
+}
+
+#[allow(dead_code)]
+#[inline(always)]
+#[cfg(target_arch = "x86_64")]
+pub fn is_windows_nt() -> bool {
+    true // let me know once someone ported 9x to 64bit LOL
+}
+
+pub fn init_rust9x_checks() {
+    // DO NOT do anything interesting or complicated in this function! DO NOT call
+    // any Rust functions or CRT functions if those functions touch any global state,
+    // because this function runs during global initialization. For example, DO NOT
+    // do any dynamic allocation, don't call LoadLibrary, etc.
+
+    init_windows_version_check();
+}
+
+static mut IS_NT: bool = true;
+
+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 };
+}