Fix UB in string.bench.cpp.

The usage of aligned_storage failed to pass the alignment it wanted,
which caused it to have a larger size and alignment that the
std::string's it was intended to store.

This patch manually specifies the alignment, as well as cleaning up
type alias bugs.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@346779 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed