`scripts/tests hol_light` silently succeeds on unsupported host architectures

[fegge]

scripts/tests hol_light selects the proof architecture from
platform.machine() at scripts/tests:1031 through scripts/tests:1034. If
the host is not arm64, aarch64, or x86_64, the function returns at
scripts/tests:1035 through scripts/tests:1036 without printing a diagnostic,
listing proofs, or calling check_fail().

The proof of concept monkeypatches platform.machine() to return riscv64 and
executes the real scripts/tests hol_light entry point. The command exits zero
with no output.

Run:

bash ptp/pocs/poc-hol-light-unsupported-arch-exits-zero.sh

Observed output:

run_rc=0
stdout_bytes=0
stderr_bytes=0
VULNERABLE: HOL-Light tests silently passed on unsupported arch