Add fallback for SwitchToThread by using Sleep(0)

Used in `thread::yield_now`.

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

Author: seritools

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

@@ -518,6 +518,17 @@ compat_fn_with_fallback! {
         SetLastError(ERROR_CALL_NOT_IMPLEMENTED as DWORD);
         FALSE
     }
+
+    // >= NT 4+
+    // https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-switchtothread
+    pub fn SwitchToThread() -> BOOL {
+        // A value of zero causes the thread to relinquish the remainder of its time slice to any
+        // other thread of equal priority that is ready to run. If there are no other threads of
+        // equal priority ready to run, the function returns immediately, and the thread continues
+        // execution.
+        Sleep(0);
+        TRUE
+    }
 }
 
 compat_fn_optional! {

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

@@ -2549,7 +2549,6 @@ Windows.Win32.System.Threading.STARTF_USESIZE
 Windows.Win32.System.Threading.STARTF_USESTDHANDLES
 Windows.Win32.System.Threading.STARTUPINFOW
 Windows.Win32.System.Threading.STARTUPINFOW_FLAGS
-Windows.Win32.System.Threading.SwitchToThread
 Windows.Win32.System.Threading.TerminateProcess
 Windows.Win32.System.Threading.THREAD_CREATE_RUN_IMMEDIATELY
 Windows.Win32.System.Threading.THREAD_CREATE_SUSPENDED

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

@@ -408,10 +408,6 @@ extern "system" {
     pub fn SleepEx(dwmilliseconds: u32, balertable: BOOL) -> u32;
 }
 #[link(name = "kernel32")]
-extern "system" {
-    pub fn SwitchToThread() -> BOOL;
-}
-#[link(name = "kernel32")]
 extern "system" {
     pub fn TerminateProcess(hprocess: HANDLE, uexitcode: u32) -> BOOL;
 }