This patch adds the `disjoint` as keyword.

This patch sets the 'iskeyword' variable to characters found in LLVM IR
identifiers. Keywords are used in many places in vim, most notably being
treated as word boundaries for commands like 'w' and '*'. The aim with
this is to improve the navigability and editability of LLVM IR files as
now one is able to: skip over entire identifiers with motions (e.g.,
`w/e/b`); yank/delete whole identifiers (e.g., `diw`); highlight/search
for the identifier under the cursor (`*`), etc.

More complicated LLVM identifiers including quotation marks are not
supported. The 'iskeyword' variable is just a list of characters, not a
regex, and including quotation marks and all the characters permitted in
quoted identifiers would expand the scope to almost everything and
become less usable. These types of identifiers are rare by comparison.

Note that this does change how words are considered across the entire
LLVM IR file, so including strings, comments, names, etc. Given that the
majority of editing/navigating LLVM IR is working with and across
values, this is arguably a worthwhile trade-off.

The `0x[KLMHR]` syntax denotes different floating-point types: various
long doubles, half and bfloat.

See https://llvm.org/docs/LangRef.html#simple-constants for reference.

This patch updates the emacs, vim, and vscode syntax highlighters to
recognize debug records.

This defines a new kind of IR Constant that represents a ptrauth signed
pointer, as used in AArch64 PAuth.

It allows representing most kinds of signed pointer constants used thus
far in the llvm ptrauth implementations, notably those used in the
Darwin and ELF ABIs being implemented for c/c++.  These signed pointer
constants are then lowered to ELF/MachO relocations.

These can be simply thought of as a constant `llvm.ptrauth.sign`, with
the interesting addition of discriminator computation: the `ptrauth`
constant can also represent a combined blend, when both address and
integer discriminator operands are used.  Both operands are otherwise
optional, with default values 0/null.

When using the vim syntax for mir, an error occurs in nvim  when opening
multiple .mir buffers. delcommand HiLink in the mir syntax file to avoid
the issue.

To reproduce:
Open an .mir file, for example
llvm/test/Codegen/X86/expand-post-ra-pseudo.mir
Open another mir file from within nvim, for example peephole.mir
```
Error detected while processing function 335[30]..<SNR>43_callback[25]..function 335[30]..<SNR>43_callback:                                                                                                                      
line   23:                                                                                                                                                                                                                       
Vim(command):E174: Command already exists: add ! to replace it: HiLink hi def link <args>   
```

I recently moved from using vim to lunarvim. I noticed that `gcc` (lol)
wasn't able to comment out lines, because commentstring is not set.

Thanks to Chase Colman for the suggestion in
https://github.com/LunarVim/LunarVim/issues/4394.

* `dump`, added in https://github.com/llvm/llvm-project/pull/68793
* `!repr`, added in https://github.com/llvm/llvm-project/pull/68716

The keyword `assert` was missing, so I have added that too.

This patch adds a new fn attribute, `optdebug`, that specifies that
optimizations should make decisions that prioritize debug info quality,
potentially at the cost of runtime performance.

This patch does not add any functional changes triggered by this
attribute, only the attribute itself. A subsequent patch will use this
flag to disable the post-RA scheduler.