Auto merge of #44251 - kennytm:osx-backtrace, r=alexcrichton

Add libbacktrace support for Apple platforms (resubmitted)

Resubmitting #43422 rebased on the current master (cc @JohnColanduoni).

I have added an additional commit to fallback to `dladdr`-based `resolve_symbol` if `libbacktrace` returns `None`, otherwise the stack trace will be full of `<unknown>` when you forget to pass the `-g` flag (actually it seems — at least on macOS — the `dladdr` symbol is more accurate than the `libbacktrace` one).

Author: bors

src/libbacktrace/configure

@@ -11844,6 +11844,9 @@ elf*) FORMAT_FILE="elf.lo" ;;
 pecoff) FORMAT_FILE="pecoff.lo"
         backtrace_supports_data=no
 	;;
+macho*) FORMAT_FILE="macho.lo"
+        backtrace_supports_data=no
+        ;;
 *) { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: could not determine output file type" >&5
 $as_echo "$as_me: WARNING: could not determine output file type" >&2;}
    FORMAT_FILE="unknown.lo"

src/libbacktrace/configure.ac

@@ -231,6 +231,9 @@ elf*) FORMAT_FILE="elf.lo" ;;
 pecoff) FORMAT_FILE="pecoff.lo"
         backtrace_supports_data=no
 	;;
+macho*) FORMAT_FILE="macho.lo"
+        backtrace_supports_data=no
+        ;;
 *) AC_MSG_WARN([could not determine output file type])
    FORMAT_FILE="unknown.lo"
    backtrace_supported=no

src/libbacktrace/filetype.awk

@@ -3,3 +3,9 @@
 /\177ELF\002/ { if (NR == 1) { print "elf64"; exit } }
 /\114\001/    { if (NR == 1) { print "pecoff"; exit } }
 /\144\206/    { if (NR == 1) { print "pecoff"; exit } }
+/\xFE\xED\xFA\xCE/ { if (NR == 1) { print "macho32"; exit } }
+/\xCE\xFA\xED\xFE/ { if (NR == 1) { print "macho32"; exit } }
+/\xFE\xED\xFA\xCF/ { if (NR == 1) { print "macho64"; exit } }
+/\xCF\xFA\xED\xFE/ { if (NR == 1) { print "macho64"; exit } }
+/\xCA\xFE\xBA\xBE/ { if (NR == 1) { print "macho-fat"; exit } }
+/\xBE\xBA\xFE\xCA/ { if (NR == 1) { print "macho-fat"; exit } }