[llvm] [Support] Fix Process::PreventCoreFiles() when coredumps are piped (PR #83703)

[Alexander Richardson via llvm-commits]

arichardson wrote:

I considered that, but according to the manpage it means we can't ptrace the process afterwards:
> Processes that are not dumpable can not be attached via [ptrace(2)](https://man7.org/linux/man-pages/man2/ptrace.2.html) PTRACE_ATTACH; see [ptrace(2)](https://man7.org/linux/man-pages/man2/ptrace.2.html) for further details.
>
> If a process is not dumpable, the ownership of files in the process's /proc/pid directory is affected as described in [proc(5)](https://man7.org/linux/man-pages/man5/proc.5.html).

It does look like it will add to dmesg (but it already seems flooded with lots of other messages):
```
[  +0.218577] traps: bounds.cpp.tmp[244068] trap invalid opcode ip:561028d05dc9 sp:7ffddaacc640 error:0 in bounds.cpp.tmp[561028c32000+d4000]
[  +0.013130] Process 244068(bounds.cpp.tmp) has RLIMIT_CORE set to 1
[  +0.006593] Aborting core
```
Is this a dealbreak? I can see if another value avoids the coredump without spamming dmesg.



https://github.com/llvm/llvm-project/pull/83703