[PECOFF] Do not add the same library to the input graph more than once.

/defaultlib options can be specified implicitly via the .drectve section, and
it's pretty common that multiple object files add the same library, such as
user32.lib, to the input. We shouldn't add the same library multiple times.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194129 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Do not expose _noDefaultLibs. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194130 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Make /disallowlib an alias for /nodefaultlib.

I'm not sure if it is really an alias for /nodefaultlib, but I can say that
they are at least similar. Making it an alias would be better than ignoring it.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194131 91177308-0d34-0410-b5e6-96231b3b80d8