libstdc++: Tweak %c formatting for chrono types

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.

(cherry picked from commit ce89d2f3170e0d6474cee2c5cb9d478426a5b2f6)

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index f8b78daedc65868c3f3e87c06da75ae4a040b97d..eaa864b0bdcd35c4fff631a6bdcad0c6b20fae71 100644 (file)
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -799,8 +799,8 @@ 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);