[libcxxabi] Remove the unused buildit script
[libcxxabi] Remove the unused buildit script

Summary: I'm pretty sure it's not used anymore, at least it isn't used at Apple.

Reviewers: EricWF, Bigcheese

Subscribers: christof, jkorous, dexonsmith, jfb, mstorsjo, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D63297

git-svn-id: 6a9f6578bdee8d959f0ed58970538b4ab6004734@363737 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi