Stub FreeEnvironmentStringsW to just leak on NT 3.1

Yup, this function just doesn't exist on NT 3.1, so
`env::vars`/`env::vars_os` will just leak the OS-allocated buffer.

Signed-off-by: Dennis Duda <git@seri.tools>

Author: seritools

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

@@ -529,6 +529,13 @@ compat_fn_with_fallback! {
         Sleep(0);
         TRUE
     }
+
+    // >= NT 3.5+, 95+
+    // https://docs.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-freeenvironmentstringsw
+    pub fn FreeEnvironmentStringsW(env_ptr: LPWCH) -> BOOL {
+        // just leak it on NT 3.1
+        TRUE
+    }
 }
 
 compat_fn_optional! {

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

@@ -2428,7 +2428,6 @@ Windows.Win32.System.Diagnostics.Debug.M128A
 Windows.Win32.System.Diagnostics.Debug.PVECTORED_EXCEPTION_HANDLER
 Windows.Win32.System.Diagnostics.Debug.XSAVE_FORMAT
 Windows.Win32.System.Diagnostics.Debug.XSAVE_FORMAT
-Windows.Win32.System.Environment.FreeEnvironmentStringsW
 Windows.Win32.System.Environment.GetCommandLineW
 Windows.Win32.System.Environment.GetCurrentDirectoryW
 Windows.Win32.System.Environment.GetEnvironmentStringsW

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

@@ -168,10 +168,6 @@ extern "system" {
     ) -> u32;
 }
 #[link(name = "kernel32")]
-extern "system" {
-    pub fn FreeEnvironmentStringsW(penv: PCWSTR) -> BOOL;
-}
-#[link(name = "kernel32")]
 extern "system" {
     pub fn GetCommandLineW() -> PCWSTR;
 }