[libc++] Fix Windows DLL build for string.

We need to mark string::npos with _LIBCPP_FUNC_VIS on the first
in-class declaration, otherwise it might get ignored

diff --git a/libcxx/include/string b/libcxx/include/string
index 2556301..313ef9f 100644 (file)
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -785,6 +785,7 @@ private:
     __compressed_pair<__rep, allocator_type> __r_;
 
 public:
+    _LIBCPP_FUNC_VIS
     static const size_type npos = -1;
 
     _LIBCPP_INLINE_VISIBILITY basic_string()