[PATCH] libstdc++: fix memory clobbering in std::vector [PR110879]

[Jonathan Wakely]

At Marek and Jason's suggestion I've moved the new test to a subdir:

   c++: Move new test to 'opt' sub-directory

   gcc/testsuite/ChangeLog:

           * g++.dg/pr110879.C: Moved to...
           * g++.dg/opt/pr110879.C: ...here.