[lldb] Fix Linux core file tests hanging on Windows (#142143)

After https://github.com/llvm/llvm-project/pull/141670, TestLinuxCore.py
was timing out on our Windows on Arm bot.

Non-Linux core files were ok, as were Linux core files unless it was
ppc64le, riscv64 or loongarch.

I eventually noticed that it was attempting to create PlatformLinux many
times before trying PlatformAndroid, PlatformMac etc., which it should
never need to do.

The tests passed on a Linux host too, to add to the mystery.

Turns out, all I needed to do was mark those architectures as supported
in the PlatformLinux constructor. If they're not listed there we get
stuck here:
```
    // Wait for a stopped event since we just posted one above...
	printf("waiting for process to stop...\n");
    lldb::EventSP event_sp;
    StateType state =
        WaitForProcessToStop(std::nullopt, &event_sp, true, listener_sp,
                             nullptr, true, SelectMostRelevantFrame);
    printf("process stopped\n");
```
Waiting for a stop event that never comes, because it appears we try to
treat the core as a real process?
```
 DynamicLoaderPOSIXDYLD::virtual DynamicLoaderPOSIXDYLD::DidAttach pid 28147 executable '<null executable>', load_offset 0xffffffffffffffff
<...>
 Process::ShouldBroadcastEvent (000002ABC43FF4A0) Restarting process from state: stopped
 Process::PrivateResume() m_stop_id = 1, public state: unloaded private state: stopped
 Process::PrivateResume() got an error "error: elf-core does not support resuming processes".
 Process::ShouldBroadcastEvent (000002ABC43FF4A0) => new state: stopped, last broadcast state: invalid - NO
```
Some actionable feedback here would be nice, but all I care about for
now is that the tests run again.

I have not added riscv32 as that appears to only be supported for Darwin
at the moment (I expect someone will get burned by this when it is).

I think debug on these architectures worked if they were also the host
arch, if someone tried to remote debug them, I think it would have
failed.