Better implementation of GetLastError. (#20623)

Instead of calling the dynamically loaded kernel32.GetLastError, we can extract it from the TEB.
As shown by [Wine](34b1606019/include/winternl.h (L439)), the last error lives at offset 0x34 of the TEB in 32-bit Windows and at offset 0x68 in 64-bit Windows.

lib/std/Thread.zig

@@ -554,7 +554,7 @@ const WindowsThreadImpl = struct {
             0,
             null,
         ) orelse {
-            const errno = windows.kernel32.GetLastError();
+            const errno = windows.GetLastError();
             return windows.unexpectedError(errno);
         };