[libc++] Qualify calls to nullary functions like __throw_foo (#122465)

This is technically not necessary in most cases to prevent issues with ADL,
but let's be consistent. This allows us to remove the libcpp-qualify-declval
clang-tidy check, which is now enforced by the robust-against-adl clang-tidy check.
diff --git a/libcxx/src/condition_variable.cpp b/libcxx/src/condition_variable.cpp
index db60571..b374760 100644
--- a/libcxx/src/condition_variable.cpp
+++ b/libcxx/src/condition_variable.cpp
@@ -26,17 +26,17 @@
 
 void condition_variable::wait(unique_lock<mutex>& lk) noexcept {
   if (!lk.owns_lock())
-    __throw_system_error(EPERM, "condition_variable::wait: mutex not locked");
+    std::__throw_system_error(EPERM, "condition_variable::wait: mutex not locked");
   int ec = __libcpp_condvar_wait(&__cv_, lk.mutex()->native_handle());
   if (ec)
-    __throw_system_error(ec, "condition_variable wait failed");
+    std::__throw_system_error(ec, "condition_variable wait failed");
 }
 
 void condition_variable::__do_timed_wait(unique_lock<mutex>& lk,
                                          chrono::time_point<chrono::system_clock, chrono::nanoseconds> tp) noexcept {
   using namespace chrono;
   if (!lk.owns_lock())
-    __throw_system_error(EPERM, "condition_variable::timed wait: mutex not locked");
+    std::__throw_system_error(EPERM, "condition_variable::timed wait: mutex not locked");
   nanoseconds d = tp.time_since_epoch();
   if (d > nanoseconds(0x59682F000000E941))
     d = nanoseconds(0x59682F000000E941);
@@ -53,7 +53,7 @@
   }
   int ec = __libcpp_condvar_timedwait(&__cv_, lk.mutex()->native_handle(), &ts);
   if (ec != 0 && ec != ETIMEDOUT)
-    __throw_system_error(ec, "condition_variable timed_wait failed");
+    std::__throw_system_error(ec, "condition_variable timed_wait failed");
 }
 
 void notify_all_at_thread_exit(condition_variable& cond, unique_lock<mutex> lk) {