Add more fuzzing bits: partial_sort_copy, partition_copy, unique, unique_copy. No functional change to libc++; this is all test infastructure

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@316951 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed