XXX push upstream: prctl(2) is Linux-only.

Index: compose/worker/asw-main.c
--- compose/worker/asw-main.c.orig
+++ compose/worker/asw-main.c
@@ -38,7 +38,7 @@
 #include <string.h>
 #ifdef __FreeBSD__
 #include <sys/procctl.h>
-#else
+#elif defined(__linux__)
 #include <sys/prctl.h>
 #endif
 
@@ -76,7 +76,7 @@ main (int argc, char **argv)
 		int sig = SIGTERM;
 		procctl (P_PID, 0, PROC_PDEATHSIG_CTL, &sig);
 	}
-#else
+#elif defined(__linux__)
 	prctl (PR_SET_PDEATHSIG, SIGTERM);
 #endif
 
