[GOLD] Don't install branch-to-stub for TLS relaxed ERRATUM 843419 sequences on AArch64

[GOLD] Don't install branch-to-stub for TLS relaxed ERRATUM 843419 sequences on AArch64

TLS relaxation may change erratum 843419 sequences that those offending ADRP
instructions actually transformed into other instructions in which case there
is erratum 843419 risk anymore that we should avoid installing unnecessary
branch-to-stub.

gold/
        * aarch64.cc (Insn_utilities::is_mrs_tpidr_el0): New method.
        (AArch64_relobj<size, big_endian>::try_fix_erratum_843419_optimized):
        Return ture for some TLS relaxed sequences.