Added configure check for sys/reg.h.

diff --git a/server/context_i386.c b/server/context_i386.c
index 4479e32..c6a9eb4 100644
--- a/server/context_i386.c
+++ b/server/context_i386.c
@@ -10,7 +10,9 @@
 
 #include <assert.h>
 #include <errno.h>
+#ifdef HAVE_SYS_REG_H
 #include <sys/reg.h>
+#endif
 #include <sys/ptrace.h>
 #include <sys/user.h>
 #include <unistd.h>