[Mips] Add "data" symbols to the test input file. No functional changes.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@201128 91177308-0d34-0410-b5e6-96231b3b80d8
[Mips] Handle R_MIPS_COPY relocation.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@201129 91177308-0d34-0410-b5e6-96231b3b80d8