Make anonymous namespace as small as possible.

LLVM coding style says that "static" is preferred for file-scope
functions.

Differential Revision: http://reviews.llvm.org/D5323

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@217692 91177308-0d34-0410-b5e6-96231b3b80d8