[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/memory_resource.cpp b/libcxx/src/memory_resource.cpp
index ec9565f..22b5493 100644
--- a/libcxx/src/memory_resource.cpp
+++ b/libcxx/src/memory_resource.cpp
@@ -48,7 +48,7 @@
     std::byte* result = std::__libcpp_allocate<std::byte>(__element_count(bytes), align);
     if (!is_aligned_to(result, align)) {
       std::__libcpp_deallocate<std::byte>(result, __element_count(bytes), align);
-      __throw_bad_alloc();
+      std::__throw_bad_alloc();
     }
     return result;
 #endif
@@ -64,7 +64,7 @@
 // null_memory_resource()
 
 class _LIBCPP_HIDDEN __null_memory_resource_imp : public memory_resource {
-  void* do_allocate(size_t, size_t) override { __throw_bad_alloc(); }
+  void* do_allocate(size_t, size_t) override { std::__throw_bad_alloc(); }
   void do_deallocate(void*, size_t, size_t) override {}
   bool do_is_equal(const memory_resource& other) const noexcept override { return &other == this; }
 };