Change the IRObjectFile symbol iterator to be a pointer into a vector of
PointerUnions representing either IR symbols or asm symbols.
This change is in preparation for a future change for supporting multiple
modules in an IRObjectFile. Although it causes an increase in memory
consumption, we can deal with that issue separately by introducing a bitcode
symbol table.
Differential Revision: https://reviews.llvm.org/D26928
llvm-svn: 287845
e32baa0c3e