[clang] [libc++] Prevent calling the projection more than three times (PR #66315)

[Louis Dionne via cfe-commits]

================
@@ -37,9 +37,10 @@ struct __fn {
     _LIBCPP_ASSERT_UNCATEGORIZED(!bool(std::invoke(__comp, std::invoke(__proj, __high), std::invoke(__proj, __low))),
                                  "Bad bounds passed to std::ranges::clamp");
 
-    if (std::invoke(__comp, std::invoke(__proj, __value), std::invoke(__proj, __low)))
+    auto&& __projected = std::invoke(__proj, __value);
----------------
ldionne wrote:

I don't see how it could dangle. Do you mean that it will dangle if `std::invoke(__proj, __value)` returns a temporary? Rvalue references extend the lifetime of temporaries so whatever this references will live until the end of the function.

https://github.com/llvm/llvm-project/pull/66315