[ELF] Refactoring and style cleanup. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@172552 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Never allocate content to weak symbols as they may be merged away.

This is done by creating a new non-weak anonymous symbol and creating
an atom with content for that symbol. This is added after the weak symbol
so that they have the same address.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@172553 91177308-0d34-0410-b5e6-96231b3b80d8
Trailing whitespace.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@172554 91177308-0d34-0410-b5e6-96231b3b80d8