Add a _LIBCPP_CONSTEXPR that was missed in r170026.

(clang doesn't complain about this, but gcc does.  This is necessary for a
follow-up patch that will enable _LIBCPP_CONSTEXPR for gcc.)


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@209888 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/limits b/include/limits
index d917c57..2216966 100644
--- a/include/limits
+++ b/include/limits
@@ -768,7 +768,7 @@
 template <class _Tp>
     _LIBCPP_CONSTEXPR const int numeric_limits<const volatile _Tp>::digits10;
 template <class _Tp>
-    const int numeric_limits<const volatile _Tp>::max_digits10;
+    _LIBCPP_CONSTEXPR const int numeric_limits<const volatile _Tp>::max_digits10;
 template <class _Tp>
     _LIBCPP_CONSTEXPR const bool numeric_limits<const volatile _Tp>::is_signed;
 template <class _Tp>