patch 8.1.2253: using "which" to check for an executable is not reliable

Problem:    Using "which" to check for an executable is not reliable.
Solution:   Use "command -v" instead.  Also exit with error code when
            generating tags has an error. (closes #5174)
diff --git a/src/version.c b/src/version.c
index 9b4c386..2a09818 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2253,
+/**/
     2252,
 /**/
     2251,