Fix build on musl, which doesn't provide a tgkill function due to concerns of it being misused.
(e.g. outside of signal handlers)

https://www.openwall.com/lists/musl/2019/08/02/1

--- a/src/libtracker-miners-common/tracker-seccomp.c
+++ b/src/libtracker-miners-common/tracker-seccomp.c
@@ -80,6 +81,11 @@
 		goto out; \
 } G_STMT_END
 
+
+#if !defined(__GLIBC__)
+#define tgkill(pid, tid, sig) syscall(SYS_tgkill, pid, tid, sig);
+#endif
+
 static void
 sigsys_handler (gint       signal,
                 siginfo_t *info,