Adapt o3tl::temporary to C++23 P2266R1

With the recent implemenation of
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2266r1.html> "P2266R1:
Simpler implicit move" in Clang 13 trunk as
<https://github.com/llvm/llvm-project/commit/bf20631782183cd19e0bb7219e908c2bbb01a75f>
"[clang] Implement P2266 Simpler implicit move", a --with-latest-c++ build
started to fail with

> In file included from sal/rtl/random.cxx:25:
> include/o3tl/temporary.hxx:21:62: error: non-const lvalue reference to type 'double' cannot bind to a temporary of type 'double'
> template <typename T> constexpr T& temporary(T&& x) { return x; }
>                                                              ^
> sal/rtl/random.cxx:97:37: note: in instantiation of function template specialization 'o3tl::temporary<double>' requested here
>     return std::modf(random, &o3tl::temporary(double()));
>                                     ^

etc.  (And fixing that by adding the recommended static_cast then triggered a
false loplugin:redundantcast warning.)

Change-Id: I222429e9872afdedf77a07014c0a2e9e06c60b50
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/117335
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/o3tl/temporary.hxx b/include/o3tl/temporary.hxx
index 7b6c9a1f9fc7..50d006e26d0e 100644
--- a/include/o3tl/temporary.hxx
+++ b/include/o3tl/temporary.hxx
@@ -18,7 +18,7 @@ namespace o3tl
 // and some call site doesn't need the value beyond the call itself (e.g., in a call like
 // std::modf(x, &o3tl::temporary(double())) to obtain the fractional part of x, ignoring the
 // integral part).
-template <typename T> constexpr T& temporary(T&& x) { return x; }
+template <typename T> constexpr T& temporary(T&& x) { return static_cast<T&>(x); }
 template <typename T> constexpr T& temporary(T&) = delete;
 }