patch 8.1.1540: cannot build without the +eval feature
Problem: Cannot build without the +eval feature.
Solution: Define ex_const if needed.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index cc6a920..91ced52 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -296,6 +296,7 @@
# define ex_endtry ex_ni
# define ex_endfunction ex_ni
# define ex_let ex_ni
+# define ex_const ex_ni
# define ex_unlet ex_ni
# define ex_lockvar ex_ni
# define ex_unlockvar ex_ni
@@ -4852,6 +4853,7 @@
/*
* Expand file name in Ex command argument.
+ * When an error is detected, "errormsgp" is set to a non-NULL pointer.
* Return FAIL for failure, OK otherwise.
*/
int