[sanitizer][test] Clean up allow_user_segv.cpp test case (#163870)

This test case has two issues:
- it has some special treatment of SIGBUS, ostensibly to handle old
Darwin platforms, but this been silently broken for years because the
assertions only check for SEGV.
- it has `XFAIL: !compiler-rt-optimized && tsan` [*], because the null
pointer dereference will trigger an assertion (invalid app memory)
rather than a segfault.

We fix both issues by directly raising SIGSEGV. We also considerably
simplify the test case, while maintaining the core test of chaining the
segfault handlers.

[*] This test might also fail when other sanitizer runtimes are compiled
with assertions, though those combinations are not well-tested by
buildbots.

0 files changed, 0 insertions, 0 deletions