Remove repeated words from BuildingLibcxx.rst
Remove repeated words from BuildingLibcxx.rst

Summary: Remove repeated words from docs.

Reviewers: phosek

Reviewed By: phosek

Subscribers: christof

Differential Revision: https://reviews.llvm.org/D60530

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@358147 91177308-0d34-0410-b5e6-96231b3b80d8

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