Use a hardcoded constant instead of calling OpenProcessToken.

Now that Win 7 support is dropped, we can resurrect rust-lang#90144.

GetCurrentProcessToken is defined in processthreadsapi.h as:

FORCEINLINE
HANDLE
GetCurrentProcessToken (
    VOID
    )
{
    return (HANDLE)(LONG_PTR) -4;
}

Since it's very unlikely that this constant will ever change, let's just use it instead of making calls to get the same information.

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

@@ -320,22 +320,16 @@ pub fn temp_dir() -> PathBuf {
 
 #[cfg(not(target_vendor = "uwp"))]
 fn home_dir_crt() -> Option<PathBuf> {
-    unsafe {
-        // The magic constant -4 can be used as the token passed to GetUserProfileDirectoryW below
-        // instead of us having to go through these multiple steps to get a token. However this is
-        // not implemented on Windows 7, only Windows 8 and up. When we drop support for Windows 7
-        // we can simplify this code. See #90144 for details.
-        use crate::sys::handle::Handle;
-
-        let me = c::GetCurrentProcess();
-        let mut token = ptr::null_mut();
-        if c::OpenProcessToken(me, c::TOKEN_READ, &mut token) == 0 {
-            return None;
-        }
-        let _handle = Handle::from_raw_handle(token);
+        // Defined in processthreadsapi.h.
+        const CURRENT_PROCESS_TOKEN: usize = -4isize as usize;
+
         super::fill_utf16_buf(
             |buf, mut sz| {
-                match c::GetUserProfileDirectoryW(token, buf, &mut sz) {
+                match c::GetUserProfileDirectoryW(
+                    ptr::from_exposed_addr_mut(CURRENT_PROCESS_TOKEN),
+                    buf,
+                    &mut sz,
+                ) {
                     0 if api::get_last_error().code != c::ERROR_INSUFFICIENT_BUFFER => 0,
                     0 => sz,
                     _ => sz - 1, // sz includes the null terminator