This change ensures that the .dynsym section will be parsed even when there's already is a .symtab.
It is motivated because of minidebuginfo (https://sourceware.org/gdb/current/onlinedocs/gdb/MiniDebugInfo.html#MiniDebugInfo).
There it says:
Keep all the function symbols not already in the dynamic symbol table.
That means the .symtab embedded inside the .gnu_debugdata does NOT contain the symbols from .dynsym. But in order to put a breakpoint on all symbols we need to load both.
To not add symbols that where already added I keep a list of unique ELF symbols on each invocation of ObjectFileELF::GetSymtab.
My other patch D66791 implements support for minidebuginfo, that's why I need this change.