Replace sigignore(<SIG>) with signal(<SIG>, SIG_IGN) (#36)
Replace sigignore(<SIG>) with signal(<SIG>, SIG_IGN) (#36)

- sigignore is deprecated and generates warning in GCC 12
- include cstring in Backtrace.hh for strlen
jrmadsen/PTL,jrmadsen/PTL,jrmadsen/PTL,jrmadsen/PTL