[PECOFF] Do not set the entry address if /noentry option is given.

This is the first step towards DLL creation support. Resource-only DLLs
don't have entry point address.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@195510 91177308-0d34-0410-b5e6-96231b3b80d8