Fix internal error caused by IFUNC patch.

Fix internal error caused by IFUNC patch.

The previous commit to fix PR gold/18886 converted STT_IFUNC
to STT_FUNC when resolving to a symbol defined in a shared library.
This leads to an internal error if the shared library symbol is
seen first, as we do not convert the symbol at all.

We need to override the STT_IFUNC in add_from_dynobj() instead of
in override_base().

gold/
	PR gold/18930
	PR gold/18886
	* resolve.cc (Symbol::override_base): Don't convert IFUNC symbols here.
	* symtab.cc (Symbol_table::add_from_dynobj): Convert them here instead.