Fix typos throughout the license files that somehow I and my reviewers

all missed!

Thanks to Alex Bradbury for pointing this out, and the fact that I never
added the intended `legacy` anchor to the developer policy. Add that
anchor too. With hope, this will cause the links to all resolve
successfully.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@351731 91177308-0d34-0410-b5e6-96231b3b80d8