Snippets for a2jmidid 9 from Alpine s390x

Sourced from https://build.alpinelinux.org/buildlogs/build-edge-s390x/testing/a2jmidid/a2jmidid-9-r3.log.

../sigsegv.c:68:12: warning: unused variable 'sz' [-Wunused-variable]
   68 |     size_t sz;
      |            ^~

../sigsegv.c:67:12: warning: unused variable 'strings' [-Wunused-variable]
   67 |     char **strings;
      |            ^~~~~~~

../sigsegv.c:66:11: warning: unused variable 'bt' [-Wunused-variable]
   66 |     void *bt[20];
      |           ^~

../log.h:47:36: warning: iteration 16 invokes undefined behavior [-Waggressive-loop-optimizations]
   47 | #define a2j_error(format, args...) a2j_log(A2J_LOG_LEVEL_ERROR, ANSI_COLOR_RED "ERROR: " ANSI_RESET "%s: " format "\n", __func__, ## args)
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

../jack.c:64:18: warning: variable 'now' set but not used [-Wunused-but-set-variable]
   64 |   jack_nframes_t now;
      |                  ^~~

../jack.c:326:7: warning: variable 'err' set but not used [-Wunused-but-set-variable]
  326 |   int err;
      |       ^~~