A change to sys/siginfo.h added a #define for si_id that breaks the vim
build.  This is a nasty hack to undo those effects, and should not go
upstream.  The right fix may be to get vim to stop using the "si_" prefix,
since that appears to be "reserved for the implementation", per the
OpenGroup specs.

--- src/syntax.c	Sat Aug 10 06:00:24 2013
+++ src/syntax.c	Wed Jan  6 10:34:12 2016
@@ -279,6 +279,7 @@
  * When si_m_endpos.lnum is 0, the items other than si_idx are unknown.
  * (The end positions have the column number of the next char)
  */
+#undef si_id
 typedef struct state_item
 {
     int		si_idx;			/* index of syntax pattern or