Handle non-PLT GNU IFUNC relocations in rtld

rtld: Apply relro to itself.

rtld: Parse own phdr and notes.

rtld: Allow to load ET_DYN && DF_1_PIE when tracing.

rtld: Add debug line for dlopen_object().

Systematically pass RTLD_LO_TRACE to load_needed_objects().

rtld: set osrel when in the direct exec mode.

Do not allow to load ET_DYN object with DF_1_PIE flag set.

rtld direct exec: add -b and -v options.

Change link_map::l_addr to mean load offset in ABI-compatible way.
Add link_map::l_refname.
Add rtld feature indicators.