Run have_func with the header providing the declarations

Author: nobu

ext/io/wait/extconf.rb

@@ -5,8 +5,8 @@
   File.write("Makefile", dummy_makefile($srcdir).join(""))
 else
   target = "io/wait"
-  have_func("rb_io_wait")
-  have_func("rb_io_descriptor")
+  have_func("rb_io_wait", "ruby/io.h")
+  have_func("rb_io_descriptor", "ruby/io.h")
   unless macro_defined?("DOSISH", "#include <ruby.h>")
     have_header(ioctl_h = "sys/ioctl.h") or ioctl_h = nil
     fionread = %w[sys/ioctl.h sys/filio.h sys/socket.h].find do |h|