[gcc r13-3890] libstdc++: Add missing definition for <charconv> in C++14 mode

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:f54ae4da1f60f4a2dea22ef184941d953442b86d

commit r13-3890-gf54ae4da1f60f4a2dea22ef184941d953442b86d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 10 14:08:49 2022 +0000

    libstdc++: Add missing definition for <charconv> in C++14 mode
    
    We support <charconv> in C++14 as an extension, but that means that
    constexpr static data members are not implicitly inline. Add an
    out-of-class definition for C++14 mode.
    
    This fixes a FAIL when -std=gnu++14 is used:
    FAIL: 20_util/from_chars/1.cc (test for excess errors)
    
    libstdc++-v3/ChangeLog:
    
            * include/std/charconv (__from_chars_alnum_to_val_table::value):
            [!__cpp_inline_variables]: Add non-inline definition.

Diff:
---
 libstdc++-v3/include/std/charconv | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index 09163af7fc9..acad865f8aa 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -444,6 +444,12 @@ namespace __detail
       static constexpr type value = (_DecOnly, _S_make_table());
     };
 
+#if ! __cpp_inline_variables
+  template<bool _DecOnly>
+    const typename __from_chars_alnum_to_val_table<_DecOnly>::type
+      __from_chars_alnum_to_val_table<_DecOnly>::value;
+#endif
+
   // If _DecOnly is true: if the character is a decimal digit, then
   // return its corresponding base-10 value, otherwise return a value >= 127.
   // If _DecOnly is false: if the character is an alphanumeric digit, then