[gcc] Deleted branch 'kmatsui/heads/is_signed' in namespace 'refs/users'

[Ken Matsui]

The branch 'kmatsui/heads/is_signed' in namespace 'refs/users' was deleted.
It previously pointed to:

 8e56cfff3641... libstdc++: use new built-in trait __is_signed

Diff:

!!! WARNING: THE FOLLOWING COMMITS ARE NO LONGER ACCESSIBLE (LOST):
-------------------------------------------------------------------

  8e56cff... libstdc++: use new built-in trait __is_signed
  457e17a... c++, libstdc++: implement __is_signed built-in trait