Protect typedef int error_t by an additional

#ifndef. Thanks Alex S. Moore <asmoore@edge.net> for helping
find the problem.

@@ -29,10 +29,12 @@
 #define __need_error_t
 #include <errno.h>
 
+#ifndef error_t
 #ifndef __error_t_defined
 typedef int error_t;
 # define __error_t_defined
 #endif
+#endif
 
 /* My libc doesn't have these.  -mccallum@jprc.com */
 #ifndef HAVE_PROGRAM_INVOCATION_NAME