[libc] fix build errors (llvm#95600)

Bitfield conversion problem tested at: https://godbolt.org/z/dxjhs5Ghr

Author: SchrodingerZhu

libc/src/__support/threads/linux/rwlock.h

@@ -370,8 +370,9 @@ class RwLock {
 public:
   LIBC_INLINE constexpr RwLock(Role preference = Role::Reader,
                                bool is_pshared = false)
-      : is_pshared(is_pshared), preference(static_cast<unsigned>(preference)),
-        state(0), writer_tid(0), queue() {}
+      : is_pshared(is_pshared),
+        preference(static_cast<unsigned>(preference) & 1u), state(0),
+        writer_tid(0), queue() {}
 
   [[nodiscard]]
   LIBC_INLINE LockResult try_read_lock() {

libc/test/integration/src/pthread/pthread_rwlock_test.cpp

@@ -37,7 +37,6 @@
 #include "src/unistd/fork.h"
 #include "test/IntegrationTest/test.h"
 #include <errno.h>
-#include <optional>
 #include <pthread.h>
 #include <time.h>