patch 8.1.1913: not easy to compute the space on the command line

Problem:    Not easy to compute the space on the command line.
Solution:   Add v:echospace. (Daniel Hahler, closes #4732)
diff --git a/src/vim.h b/src/vim.h
index 254d3ef..dca8748 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1981,7 +1981,8 @@
 #define VV_TERMBLINKRESP 89
 #define VV_EVENT	90
 #define VV_VERSIONLONG	91
-#define VV_LEN		92	// number of v: vars
+#define VV_ECHOSPACE	92
+#define VV_LEN		93	// number of v: vars
 
 // used for v_number in VAR_SPECIAL
 #define VVAL_FALSE	0L