patch 8.2.2021: Vim9: get E1099 when autocommand resets did_emsg

Problem:    Vim9: get E1099 when autocommand resets did_emsg.
Solution:   Add did_emsg_cumul. (closes #7336)
diff --git a/src/globals.h b/src/globals.h
index dd7fa4a..af1a85c 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -230,6 +230,8 @@
 EXTERN int	did_emsg;		    // set by emsg() when the message
 					    // is displayed or thrown
 #ifdef FEAT_EVAL
+EXTERN int	did_emsg_cumul;		    // cumulative did_emsg, increased
+					    // when did_emsg is reset.
 EXTERN int	called_vim_beep;	    // set if vim_beep() is called
 EXTERN int	did_uncaught_emsg;	    // emsg() was called and did not
 					    // cause an exception