[gcc r14-6493] libstdc++: Fix regression in std::format output of %Y for negative years

[Jonathan Wakely]

https://gcc.gnu.org/g:ad537ccd525fd3af759febd6c0936f82de808a70

commit r14-6493-gad537ccd525fd3af759febd6c0936f82de808a70
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Dec 13 12:00:45 2023 +0000

    libstdc++: Fix regression in std::format output of %Y for negative years
    
    The change in r14-6468-ga01462ae8bafa8 was only supposed to apply to %C
    formats, not %Y.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/chrono_io.h (__formatter_chrono::_M_C_y_Y): Do
            not round century down for %Y formats.

Diff:
---
 libstdc++-v3/include/bits/chrono_io.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index b63b8592eba..bcd76e4ab7b 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -825,7 +825,7 @@ namespace __format
 		{
 		  __s.assign(1, _S_plus_minus[1]);
 		  // For floored division -123//100 is -2 and -100//100 is -1
-		  if ((__ci * 100) != __yi)
+		  if (__conv == 'C' && (__ci * 100) != __yi)
 		    ++__ci;
 		}
 	      if (__ci >= 100) [[unlikely]]