[experiment]: Use capstone to implement ELF.libc_start_main_ret

[tesuji]

Use capstone to implement ELF.libc_start_main_ret.

Reasons:

• Avoid text-based searching on objdump's output to ease maintenance.
• Make it easier to support other architectures.
  powerpc64 still fail after this PR.
• For fun.

I marked this PR as draft to get some early feedback, and some volunteer testers.

Testing

Need more testing!!! And some design works to make the code cleaner.

This PR has been manually tested on (✓ is pass, X is failure):

arch	2.28	2.36	2.31
x86_64	✓	✓
i386	✓	✓
mips	✓	✓
mips64el	✓	✓
arm64	✓	✓
armel	✓	✓
armhf	✓	✓
ppc64el	✓	✓	✓
s390	N/A	✓	✓

Failure cases:

• mips: Not really fail but upgrading capstone to v6.alpha should remove a condition.

Failure arch on dev:

• armhf:
  Fail to decompile this target, this should use arm-linux-gnueabihf-objdump.