GH-135904: Implement assembler optimization for AArch64.

[markshannon]

Implements #135904 for AArch64 to match the optimisation for x86.
Removes a number of unnecessary branches.

• Issue: Optimize the JIT's low-level assembly control flow #135904

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[markshannon]

It looks like there are three issues here:

• The R_AARCH64_TSTBR14 relocation only allows a jump of 2**15 bytes, which is not enough for the JIT in debug mode. We could maybe workaround this, as it would be nice to have for the release build. But I think we can just drop support for optimising cbz and tbz instructions for now.
• We don't have the symbol name for 19 bit relocations on Windows. This is an easy fix.
• The llvm assembler is rejecting b.eq __JIT_ERROR_TARGET because "conditional branch requires assembler-local label", but the code is fine. This might be because the home-brew installed llvm is too old?

[diegorusso]

Thanks for the PR and for finally implement this. It was in my todo list for long time :) @brandtbucher would be happy to see this implemented.

Of course this is OK (I've reviewed this internally at Arm)

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x (tier-2) has failed when building commit f188385.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/725/builds/12123) and take a look at the build logs.
4. Check if the failure is related to this commit (f188385) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/725/builds/12123

Failed tests:

• test_urllib2net

Failed subtests:

• test_ftp - test.test_urllib2net.OtherNetworkTests.test_ftp

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_urllib2net.py", line 239, in _test_urls
    f = urlopen(url, req, support.INTERNET_TIMEOUT)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_urllib2net.py", line 28, in wrapped
    return _retry_thrice(func, exc, *args, **kwargs)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_urllib2net.py", line 24, in _retry_thrice
    raise last_exc
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_urllib2net.py", line 20, in _retry_thrice
    return func(*args, **kwargs)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/urllib/request.py", line 487, in open
    response = self._open(req, data)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/urllib/request.py", line 504, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
                              '_open', req)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/urllib/request.py", line 464, in _call_chain
    result = func(*args)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/urllib/request.py", line 1556, in ftp_open
    raise URLError(f"ftp error: {exp}") from exp
urllib.error.URLError: <urlopen error ftp error: timed out>


Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/urllib/request.py", line 1546, in ftp_open
    fp, retrlen = fw.retrfile(file, type)
                  ~~~~~~~~~~~^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/urllib/request.py", line 1806, in retrfile
    conn, retrlen = self.ftp.ntransfercmd(cmd)
                    ~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/ftplib.py", line 354, in ntransfercmd
    conn = socket.create_connection((host, port), self.timeout,
                                    source_address=self.source_address)
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/socket.py", line 879, in create_connection
    raise exceptions[0]
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/socket.py", line 864, in create_connection
    sock.connect(sa)
    ~~~~~~~~~~~~^^^^
TimeoutError: timed out