[ELF] Support TLS GD/LD relaxations for x86-32 -fno-plt

For x86-32, {clang,gcc} -fno-plt uses `call *___tls_get_addr@GOT(%reg)` instead
of `call ___tls_get_addr@PLT`. GD to IE/LE relaxations need to shift the offset
by one while LD to LE relaxation needs to use a different code sequence.

While here, fix some comments.

Fix https://github.com/llvm/llvm-project/issues/59769

Differential Revision: https://reviews.llvm.org/D140813