BT_STACK_SZ and backtrace_buffer are not used when
HAVE_BACKTRACE is undefined. Wrap them in #ifdef
to avoid a build warning:
../lib/fuse_signals.c:31:14: warning: 'backtrace_buffer' defined but not used [-Wunused-variable]
31 | static void *backtrace_buffer[BT_STACK_SZ];
| ^~~~~~~~~~~~~~~~
[1] https://github.com/libfuse/libfuse/pull/1245
Signed-off-by: Georgi Valkov <gvalkov@gmail.com>