[clang] __builtin_verbose_trap should optionally also accept an immediate to emit

This would allow identifying where the trap came from even when no debug information is available. This would provide the same functionality that `__builtin_arm_trap` provides, but to `__builtin_verbose_trap`.

Start by locating the implementation and tests for __builtin_verbose_trap, then compare how __builtin_arm_trap handles an immediate argument. Add coverage for the optional immediate and verify that the resulting trap can identify its origin without debug information.

Written by the indexing model from the issue text.