Bugfixes in MORELLO GOT relocations

Bugfixes in MORELLO GOT relocations

Trying to link code against newlib with the current BFD Morello linker
we get quite a lot of cases of the error below.
 "relocation truncated to fit: R_MORELLO_LD128_GOT_LO12_NC against symbol
 `<whatever>' defined in .text.<whatever> section in <filename>"

This happens because the relocation gets transformed into a relocation
pointing into the GOT in elfNN_aarch64_final_link_relocate, but the
h->target_internal flag that indicates whether this is a C64 function
symbol or not is then added to the *end* value rather than the value
that is stored in the GOT.

This then correctly falls foul of a check in _bfd_aarch64_elf_put_addend
that ensures the value we get from this relocation is 8-byte aligned
since it must be pointing to the start of a valid entry in the GOT.

Here we ensure that this LSB is set on the value newly added into the
GOT rather than on the offset pointing into the GOT.  This both means
that loading function symbols from the GOT will have the LSB correctly
set (hence we stay in C64 mode when branching to this function as we
should) and it means that the error about a misaligned GOT address is
fixed.

In this patch we also ensure that we add a dynamic relocation to
initialise the correct GOT entry when we are resolving a MORELLO
relocation that requires an entry in the GOT.
This was already handled in the case of a global symbol, but had not
been handled in the case of a local symbol.  This is why we set
`relative_reloc` to TRUE in if resolving a MORELLO GOT relocation
against a static executable.

In writing the testcase for this patch we found an existing bug to do
with static relocations of this kind (of this kind meaning that are
handled in this case statement).  The assembler often chooses to create
the relocation against the section symbol rather than the original
symbol, and make up for that by giving the relocation an addend.  The
linker does not have any mechanism to create "symbol plus addend"
entries in the GOT -- it indexes into the GOT based on the symbol only.
Hence all relocations which are a section symbol plus addend end up
pointing at one value in the GOT just containing the value of the
symbol.
We do not fix this existing bug, but just note it given that this is in the
same area.