[libstdc++] drop workaround for clang<=7

In response to a request in the review of the patch that introduced
_GLIBCXX_CLANG, this patch removes from std/variant an obsolete
workaround for clang 7-.

for  libstdc++-v3/ChangeLog

	* include/std/variant: Drop obsolete workaround.

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 51aaa62085170150923e55bbf73d560b58af93a1..13ea1dd3849657c0e3c4482794e317fb6a291dc1 100644 (file)
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1758,11 +1758,6 @@ namespace __detail::__variant
          }, __rhs);
       }
 
-#if defined(_GLIBCXX_CLANG) && __clang_major__ <= 7
-    public:
-      using _Base::_M_u; // See https://bugs.llvm.org/show_bug.cgi?id=31852
-#endif
-
     private:
       template<size_t _Np, typename _Vp>
        friend constexpr decltype(auto)