workaround while we get it fixed upstream

http://bugs.gentoo.org/201114

--- libbb/u_signal_names.c
+++ libbb/u_signal_names.c
@@ -66,7 +66,7 @@
 #ifdef SIGTERM
 	[SIGTERM  ] = "TERM",
 #endif
-#ifdef SIGSTKFLT
+#if defined(SIGSTKFLT) && SIGSTKFLT < 32
 	[SIGSTKFLT] = "STKFLT",
 #endif
 #ifdef SIGCHLD
@@ -90,10 +90,10 @
 #ifdef SIGURG
 	[SIGURG   ] = "URG",
 #endif
-#ifdef SIGXCPU
+#if defined(SIGXCPU) && SIGXCPU < 32
 	[SIGXCPU  ] = "XCPU",
 #endif
-#ifdef SIGXFSZ
+#if defined(SIGXFSZ) && SIGXFSZ < 32
 	[SIGXFSZ  ] = "XFSZ",
 #endif
 #ifdef SIGVTALRM
