Add benchmarks for sorting and heap functions.
Add benchmarks for sorting and heap functions.

Summary:
Benchmarks for std::sort, std::stable_sort, std::make_heap,
std::sort_heap, std::pop_heap and std::push_heap.

The benchmarks are run with integers and strings, and with different
sorted input.

Reviewers: EricWF

Subscribers: christof, mgrang, ldionne, libcxx-commits

Differential Revision: https://reviews.llvm.org/D53978

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@347329 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx