Cleanup: move visibility/linkage attributes to the first declaration.

This change moves visibility attributes from out-of-class method
definitions to in-class declaration. This is needed for a switch to
attribute((internal_linkage)) (see http://reviews.llvm.org/D13925)
which can only appear on the first declaration.

This change does not touch istream/ostream/streambuf. They are
handled separately in http://reviews.llvm.org/D14409.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@252385 91177308-0d34-0410-b5e6-96231b3b80d8

include/thread

@@ -318,6 +318,7 @@ public:
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
     _LIBCPP_INLINE_VISIBILITY
     thread(thread&& __t) _NOEXCEPT : __t_(__t.__t_) {__t.__t_ = 0;}
+    _LIBCPP_INLINE_VISIBILITY
     thread& operator=(thread&& __t) _NOEXCEPT;
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -399,7 +400,7 @@ thread::thread(_Fp __f)
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
-inline _LIBCPP_INLINE_VISIBILITY
+inline
 thread&
 thread::operator=(thread&& __t) _NOEXCEPT
 {