Propagate required tool-probe failures from native ARM64 diagnostics

[LunaStev]

Source-audit reproduction

The native diagnostic helper runs compiler-version, default-target, LLVM-version, and debugger-version probes but discards every return value. It initializes failed = False afterward. As a result, its final result can claim success despite failed compiler/toolchain probes.

I exercised the actual main() control flow in an isolated temporary directory with an ARM64 PE header and injected probe results. Returning 7 for all four version/target probes and 0 for the check/build probes yields overall exit 0. No repository source was modified for the reproduction.

The actual PR #574 native job had successful version probes and failed compilation; this additional bug was found by auditing that diagnostic path, not claimed as its observed failure cause.

Acceptance

• Identify required compiler/target/LLVM probes and propagate their failure to the final diagnostic status.
• Report unavailable debugger capability explicitly; decide whether it is mandatory when crash collection is needed instead of silently discarding its result.
• Continue collecting useful independent evidence after a probe failure while retaining the failure status.
• Add injected-probe tests for nonzero exit, launch failure, timeout, and successful required probes.

Keep this scoped to diagnostic status handling. The compiler access violation remains #493; existing PowerShell smoke exit handling is tracked in #505.