[libc] Add template deduction guide for cpp::lock_guard. (#91589)

Fix ctad-maybe-unsupported warnings for `cpp::lock_guard`.

Author: lntue

libc/src/__support/CPP/mutex.h

@@ -40,6 +40,9 @@ template <typename MutexType> class lock_guard {
   lock_guard(const lock_guard &) = delete;
 };
 
+// Deduction guide for lock_guard to suppress CTAD warnings.
+template <typename T> lock_guard(T &) -> lock_guard<T>;
+
 } // namespace cpp
 } // namespace LIBC_NAMESPACE