[PATCH] libstdc++: Tweak %c formatting for chrono types

[Jonathan Wakely]

Tested x86_64-linux.

-- >8 --

libstdc++-v3/ChangeLog:

        * include/bits/chrono_io.h (__formatter_chrono::_M_c): Add
        [[unlikely]] attribute to condition for missing %c format in
        locale. Use %T instead of %H:%M:%S in fallback.
---
 libstdc++-v3/include/bits/chrono_io.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/chrono_io.h 
b/libstdc++-v3/include/bits/chrono_io.h
index a337007266e..652e88ffe3a 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -899,8 +899,8 @@ namespace __format
          const _CharT* __formats[2];
          __tp._M_date_time_formats(__formats);
          const _CharT* __rep = __formats[__mod];
-         if (!*__rep)
-           __rep = _GLIBCXX_WIDEN("%a %b %e %H:%M:%S %Y");
+         if (!*__rep) [[unlikely]]
+           __rep = _GLIBCXX_WIDEN("%a %b %e %T %Y");
          basic_string<_CharT> __fmt(_S_empty_spec);
          __fmt.insert(1u, 1u, _S_colon);
          __fmt.insert(2u, __rep);
-- 
2.46.1