patch 8.0.0451: some macros are in lower case

Problem:    Some macros are in lower case.
Solution:   Make a few more macros upper case. Avoid lower case macros use an
            argument twice.
diff --git a/src/proto/misc2.pro b/src/proto/misc2.pro
index 83384c0..68c40da 100644
--- a/src/proto/misc2.pro
+++ b/src/proto/misc2.pro
@@ -83,7 +83,7 @@
 int after_pathsep(char_u *b, char_u *p);
 int same_directory(char_u *f1, char_u *f2);
 int vim_chdirfile(char_u *fname);
-int illegal_slash(char *name);
+int vim_stat(const char *name, stat_T *stp);
 char_u *parse_shape_opt(int what);
 int get_shape_idx(int mouse);
 void update_mouseshape(int shape_idx);