Fix gdb backtrace command
Fix gdb backtrace command

Correct the command to get a gdb backtrace from all threads. `apply` is
not a valid gdb command.

See https://sourceware.org/gdb/onlinedocs/gdb/Threads.html#Threads .
openwide-java/gitlabhq,daiyu/gitlab-zh,axilleas/gitlabhq,mmkassem/gitlabhq,darkrasid/gitlabhq,dreampet/gitlab,LUMC/gitlabhq,htve/GitlabForChinese,t-zuehlsdorff/gitlabhq,openwide-java/gitlabhq,dplarson/gitlabhq,dreampet/gitlab,darkrasid/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,LUMC/gitlabhq,daiyu/gitlab-zh,mmkassem/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,openwide-java/gitlabhq,jirutka/gitlabhq,stoplightio/gitlabhq,t-zuehlsdorff/gitlabhq,darkrasid/gitlabhq,LUMC/gitlabhq,t-zuehlsdorff/gitlabhq,daiyu/gitlab-zh,t-zuehlsdorff/gitlabhq,iiet/iiet-git,openwide-java/gitlabhq,iiet/iiet-git,htve/GitlabForChinese,iiet/iiet-git,jirutka/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,dplarson/gitlabhq,jirutka/gitlabhq,dplarson/gitlabhq,darkrasid/gitlabhq,htve/GitlabForChinese,dreampet/gitlab,axilleas/gitlabhq,iiet/iiet-git,daiyu/gitlab-zh,stoplightio/gitlabhq,htve/GitlabForChinese,LUMC/gitlabhq