patch 9.1.0818: some global functions are only used in single files

Problem:  some global functions are only used in single files
Solution: refactor code slightly and make some more functions static
          (Yegappan Lakshmanan)

closes: #15951

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/misc1.c b/src/misc1.c
index 0898efb..90cf914 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -953,6 +953,17 @@
     return n;
 }
 
+// For overflow detection, add a digit safely to an int value.
+    static int
+vim_append_digit_int(int *value, int digit)
+{
+    int x = *value;
+    if (x > ((INT_MAX - digit) / 10))
+	return FAIL;
+    *value = x * 10 + digit;
+    return OK;
+}
+
 /*
  * Get a number from the user.
  * When "mouse_used" is not NULL allow using the mouse.
@@ -2824,17 +2835,6 @@
 #endif
 }
 
-// For overflow detection, add a digit safely to an int value.
-    int
-vim_append_digit_int(int *value, int digit)
-{
-    int x = *value;
-    if (x > ((INT_MAX - digit) / 10))
-	return FAIL;
-    *value = x * 10 + digit;
-    return OK;
-}
-
 // For overflow detection, add a digit safely to a long value.
     int
 vim_append_digit_long(long *value, int digit)