This patch uses a "belt & suspenders" approach: either the inclusion of
<sys/types.h> before the define, or changing the variable name is sufficient,
but both are used out of precaution.  The patch was developed in-house;
the changing of the variable name part has been fed upstream and will be
included in the next version.

--- xmlto-0.0.28/xmlif/xmlif.c.~1~	2015-11-10 04:05:27.000000000 -0800
+++ xmlto-0.0.28/xmlif/xmlif.c	2016-03-14 13:33:03.905766962 -0700
@@ -20,6 +20,7 @@
 #include <string.h>
 #include <errno.h>
 #include <stdlib.h>
+#include <sys/types.h>
 
 /* end standard C headers. */
 
@@ -1306,7 +1307,7 @@
 
 #define INITIAL 0
 #define attrib 1
-#define val 2
+#define xmlif_val 2
 
 #ifndef YY_NO_UNISTD_H
 /* Special case for "unistd.h", since it is non-ANSI. We include it way
@@ -1594,7 +1595,7 @@
 case 8:
 YY_RULE_SETUP
 #line 217 "xmlif/xmlif.l"
-{BEGIN(val);}
+{BEGIN(xmlif_val);}
 	YY_BREAK
 case 9:
 YY_RULE_SETUP
@@ -1636,7 +1637,7 @@
 #line 1637 "xmlif/xmlif.c"
 case YY_STATE_EOF(INITIAL):
 case YY_STATE_EOF(attrib):
-case YY_STATE_EOF(val):
+case YY_STATE_EOF(xmlif_val):
 	yyterminate();
 
 	case YY_END_OF_BUFFER: