bump libbacktrace-upstream to `14818b7783eeb9a56c3f0fca78cefd3143f8…

…c5f6` (#30)

- config/override.m4: don't require exactly autoconf 2.69
- configury: update to recent versions
- configury: support --disable-werror
- libbacktrace: initialize DWARF 5 fields of unit
- libbacktrace: gather address ranges from skeleton units
- libbacktrace: don't skip initial aligned byte in uncompressed block
- libbacktrace: replace fgrep with grep in configure script
- libbacktrace: don't let "make clean" remove allocfail.sh
- libbacktrace: don't exit Mach-O dyld library loop on one failure
- libbacktrace: check for sys/link.h
- libbacktrace: support zstd decompression
- libbacktrace: rewrite and simplify main zstd loop
- libbacktrace: unpack literals into output buffer
- libbacktrace: don't run --build-id tests if it is not supported
- libbacktrace: change PC variables from uint64_t to uintptr_t
- libbacktrace: minor fixes for zstd decompression
- libbacktrace: look for _pgmptr on Windows
- [libbacktrace] fix up broken test
- libbacktrace: call GetModuleFileNameA on Windows
- libbacktrace: support ASLR on Windows