Some maintenance on implementation and tests:
* Drop manual TargetMachineBuilder setup
* Drop addDebugSupport() in favor of Orc's enableDebuggerSupport()
* Check that debug support plugins append jit_code_entry
* Update and reduce sample input
https://github.com/llvm/llvm-project/pull/74764 reported that the
`lljit-with-remote-debugging` test fails on AArch64 hosts, because the
input IR file states arch x86_64 explicitly. In order to drop the target
triple we have to remove a check in the example implementation.
Not sure it's fully portable now, but at least it's better than before.
Though this is a full port of the example, it is not yet fully functional due to a threading issue in the SimpleRemoteEPC implementation. The issue was discussed in D110530, but it needs a more thorough solution. For now we are dropping the dependency to the old `OrcRPC` here (it's been the last use-case in-tree). The test for the example is under review in ... and will be re-enabled once the threading issue is solved.
