[libc++] Remove workaround for D63883

I tried applying D63883 three times and could never get around to
making it work. I'm giving up on that for now, but soon this should
be irrelevant anyway since all builds will move to the monorepo
(where we're always using the in-tree libc++abi unless explicitly
specified otherwise).

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@373384 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed