Handle R_GENERIC_TLS_TPREL relocations

This relocation is used for static TLS's initial-exec (IE) accesses.

A TLS symbol's value is its offset from the start of the ELF module's
TLS segment. It doesn't make sense to add the load_bias to this value,
so skip the call to soinfo::resolve_symbol_address.

Allow TLS relocations to refer to an unresolved weak symbol. In that case,
sym will be non-zero, but lsi will be nullptr. The dynamic linker resolves
the TPREL relocation to 0, making &missing_weak_symbol equal the thread
pointer.

Recognize Gold-style relocations to STB_LOCAL TLS symbols/sections and
issue an error.

Remove the "case R_AARCH64_TLS_TPREL64", because the R_GENERIC_TLS_TPREL
case handles it.

Remove the no-op R_AARCH64_TLSDESC handler. It's better to issue an error.
dlopen_library_with_ELF_TLS now fails with a consistent error about an
unimplemented dynamic TLS relocation.

Bug: http://b/78026329
Test: bionic unit tests (elftls tests are added in a later CL)
Change-Id: Ia08e1b5c8098117e12143d3b4ebb4dfaa5ca46ec