suppress gcc 8 aliasing warnings

function                                             old     new   delta
sigprocmask_SIG_SETMASK                                -      16     +16
wait_for_child_or_signal                             221     213      -8
dowait                                               432     424      -8

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/signals.c b/libbb/signals.c
index 3f58932..5a1544d 100644
--- a/libbb/signals.c
+++ b/libbb/signals.c
@@ -31,6 +31,16 @@
 	return sigprocmask(how, &set, NULL);
 }
 
+int FAST_FUNC sigprocmask_SIG_SETMASK(sigset_t *set)
+{
+	// Grr... gcc 8.1.1:
+	// "passing argument 3 to restrict-qualified parameter aliases with argument 2"
+	// dance around that...
+	sigset_t *oset FIX_ALIASING;
+	oset = set;
+	return sigprocmask(SIG_SETMASK, set, oset);
+}
+
 void FAST_FUNC bb_signals(int sigs, void (*f)(int))
 {
 	int sig_no = 0;