patch 8.0.0074
Problem:    Cannot make Vim fail on an internal error.
Solution:   Add IEMSG() and IEMSG2(). (Domenique Pelle)  Avoid reporting an
            internal error without mentioning where.
diff --git a/src/proto/message.pro b/src/proto/message.pro
index 7112b09..c9d62c6 100644
--- a/src/proto/message.pro
+++ b/src/proto/message.pro
@@ -11,6 +11,12 @@
 void do_perror(char *msg);
 int emsg(char_u *s);
 int emsg2(char_u *s, char_u *a1);
+int emsg3(char_u *s, char_u *a1, char_u *a2);
+int emsgn(char_u *s, long n);
+void iemsg(char_u *s);
+void iemsg2(char_u *s, char_u *a1);
+void iemsgn(char_u *s, long n);
+void internal_error(char *where);
 void emsg_invreg(int name);
 char_u *msg_trunc_attr(char_u *s, int force, int attr);
 char_u *msg_may_trunc(int force, char_u *s);