Fix tileiras SIGSEGV with occupancy=2 by retrying without occupancy hint

[yanght27]

Description

Fix #96. tileiras can terminate with SIGSEGV (return code -11) when compiling certain kernels with an explicit occupancy hint (e.g. occupancy=2 on a 32-wide fused tile targeted at sm_120). Since occupancy is a scheduling hint, retry the compilation once with occupancy=None if the compiler crashes with SIGSEGV, and emit a UserWarning to tell the user that the hint was dropped.

Verification

• Real reproducer.
• pytest test/test_compiler_sigsegv_fallback.py: 1 passed.
• flake8: PASS.
• scripts/check_license.py: PASS.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.