Our <sys/select.h> has definition of 'sigset_t'.

Index: tests/sys_select.in.h
--- tests/sys_select.in.h.orig
+++ tests/sys_select.in.h
@@ -125,7 +125,7 @@
    undeclared error occurs in <pthread.h>.
    Do this after the include_next (for the sake of OpenBSD 5.0) but before
    the split double-inclusion guard (for the sake of Solaris).  */
-#if !((defined __GLIBC__ || defined __CYGWIN__ || defined __KLIBC__) \
+#if !((defined __GLIBC__ || defined __CYGWIN__ || defined __KLIBC__ || defined __OpenBSD__) \
       && !defined __UCLIBC__)
 # include <signal.h>
 #endif
