[libcxx] Fix include paths in fuzzing/partial_sort.pass.cpp
Summary:
When testing an installed (out-of-tree) version of libc++, the
"libcxx/fuzzing/partial_sort.pass.cpp" test fails because of missing
include files "../fuzzing/fuzzing.{h,cpp}". This happens because in
the source tree "../fuzzing" can be accessed as
"libcxx/include/../fuzzing", but with the installed library this does
not work.
This patch fixes the issue by changing the path to be relative from
the `libcxx/test/fuzzing" directory.
Reviewers: mclow.lists, EricWF, christof, michaelplatings
Reviewed By: michaelplatings
Subscribers: merge_guards_bot, ldionne, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D71459