[master] Corrected unit test build failure under Solaris 11

Reverted change to configure.ac that broke the test for sys/filio.h.
This include is needed for unit tests in dhcp_ddns.

configure.ac

@@ -913,7 +913,7 @@ if test "$MYSQL_CONFIG" != "" ; then
 fi
 
 # Solaris puts FIONREAD in filio.h
-AC_CHECK_HEADER(sys/filio.h)
+AC_CHECK_HEADERS(sys/filio.h,,,)
 
 # ... and at the shell level, so Makefile.am can take action depending on this.
 AM_CONDITIONAL(HAVE_MYSQL, test "$MYSQL_CONFIG" != "")