[COMMITTED] libstdc++: Avoid using sizeof with function types (PR 93470)

[Jonathan Wakely]

        PR libstdc++/93470
        * include/bits/refwrap.h (reference_wrapper::operator()): Restrict
        static assertion to object types.

Tested powerpc64le-linux and verified with Clang.

Committed to master. Backport to gcc-9-branch needed too.


commit 72a9fd209b6db3b5f81fbb008e22ea93c00465e5
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Jan 28 13:24:09 2020 +0000

    libstdc++: Avoid using sizeof with function types (PR 93470)
    
            PR libstdc++/93470
            * include/bits/refwrap.h (reference_wrapper::operator()): Restrict
            static assertion to object types.

diff --git a/libstdc++-v3/include/bits/refwrap.h 
b/libstdc++-v3/include/bits/refwrap.h
index 2bcd44d3894..717aa01629c 100644
--- a/libstdc++-v3/include/bits/refwrap.h
+++ b/libstdc++-v3/include/bits/refwrap.h
@@ -343,7 +343,8 @@ _GLIBCXX_MEM_FN_TRAITS(&& noexcept, false_type, true_type)
        operator()(_Args&&... __args) const
        {
 #if __cplusplus > 201703L
-         static_assert(sizeof(type), "type must be complete");
+         if constexpr (is_object_v<type>)
+           static_assert(sizeof(type), "type must be complete");
 #endif
          return std::__invoke(get(), std::forward<_Args>(__args)...);
        }