patch 8.2.0067: ERROR_UNKNOWN clashes on some systems

Problem:    ERROR_UNKNOWN clashes on some systems.
Solution:   Rename ERROR_ to FCERR_. (Ola Söder, closes #5415)
diff --git a/src/vim.h b/src/vim.h
index c4c649c..d69272e 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2551,15 +2551,15 @@
 				// be freed.
 
 // errors for when calling a function
-#define ERROR_UNKNOWN	0
-#define ERROR_TOOMANY	1
-#define ERROR_TOOFEW	2
-#define ERROR_SCRIPT	3
-#define ERROR_DICT	4
-#define ERROR_NONE	5
-#define ERROR_OTHER	6
-#define ERROR_DELETED	7
-#define ERROR_NOTMETHOD	8   // function cannot be used as a method
+#define FCERR_UNKNOWN	0
+#define FCERR_TOOMANY	1
+#define FCERR_TOOFEW	2
+#define FCERR_SCRIPT	3
+#define FCERR_DICT	4
+#define FCERR_NONE	5
+#define FCERR_OTHER	6
+#define FCERR_DELETED	7
+#define FCERR_NOTMETHOD	8   // function cannot be used as a method
 
 // flags for find_name_end()
 #define FNE_INCL_BR	1	// include [] in name