COFF: Handle /include in .drectve.

We don't want to insert a new symbol to the symbol table while reading
a .drectve section because it's going to be too complicated.
That we are reading a directive section means that we are currently
reading some object file. Adding a new undefined symbol to the symbol
table can trigger a library file to read a new file, so it would make
the call stack too deep.

In this patch, I add new symbol names to a list to resolve them later.

llvm-svn: 240076