Add first linker pass (StubsPass) which looks for calls to shared library
symbols and replaces them with calls to a StubAtom. On ELF system, a "stub"
is a PLT entry. Added a simple test case.
Pass a Platform object to YAML reader and writer for converting fixup kinds
between names and values.
Change output of Resolver to be a File object instead of a vector of Atoms.
Thus, passes operate on a File instead of just Atoms.
Rework how to walk through a File's Atoms. Now iterator based instead of
a method that visits each atom.
llvm-svn: 152269
