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/vim.h b/src/vim.h
index 5946d63..eec3e4f 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1623,6 +1623,9 @@
 #define EMSG3(s, p, q)		    emsg3((char_u *)(s), (char_u *)(p), (char_u *)(q))
 #define EMSGN(s, n)		    emsgn((char_u *)(s), (long)(n))
 #define EMSGU(s, n)		    emsgu((char_u *)(s), (long_u)(n))
+#define IEMSG(s)		    iemsg((char_u *)(s))
+#define IEMSG2(s, p)		    iemsg2((char_u *)(s), (char_u *)(p))
+#define IEMSGN(s, n)		    iemsgn((char_u *)(s), (long)(n))
 #define OUT_STR(s)		    out_str((char_u *)(s))
 #define OUT_STR_NF(s)		    out_str_nf((char_u *)(s))
 #define MSG_PUTS(s)		    msg_puts((char_u *)(s))