Open a terminal and type into it what comes after the hash ("gdb vlc"). Then type "break XOpenDisplay" once you see the "(gdb)" input line and press enter. Answer the question with "y" (yes) and press enter. Then type "break XInitThreads" and press enter. Answer the question with "y" (yes) and press enter. Then type "run" and press enter. Then vlc should crash. Then type "bt" and press enter.
Open a terminal and type into it what comes after the hash ("gdb vlc"). Then type "break XOpenDisplay" once you see the "(gdb)" input line and press enter. Answer the question with "y" (yes) and press enter. Then type "break XInitThreads" and press enter. Answer the question with "y" (yes) and press enter. Then type "run" and press enter. Then vlc should crash. Then type "bt" and press enter.