build: Add private.h to sched sources

faux/sched/Makefile.am

@@ -1,6 +1,7 @@
 libfaux_la_SOURCES += \
 	faux/sched/ev.c \
-	faux/sched/sched.c
+	faux/sched/sched.c \
+	faux/sched/private.h
 
 if TESTC
 libfaux_la_SOURCES += faux/sched/testc_sched.c