Adding a test case for pr15415 - partial backtrace with -fomit-frame-pointer
that is patterned after its parent TestInferiorCrashing.py.

- The xfail decorator limits the xfail to tool-chains that support this compiler option.
- Included a TODO concerning the platform-specific behavior when 'next' is issued after a crash.
- Toggling -fomit-frame-pointer results in an xpass as mentioned in pr15415.

Thanks to Daniel for the review, and Samuel for the bug report and reproducer.