vim-patch:8.0.0448: some macros are lower case (#7936)

Problem:    Some macros are in lower case, which can be confusing.
Solution:   Make a few lower case macros upper case.
b5aedf3e22

ref #6297

src/nvim/option.c

@@ -1059,7 +1059,7 @@ void set_init_3(void)
     xfree(p);
   }
 
-  if (bufempty()) {
+  if (BUFEMPTY()) {
     int idx_ffs = findoption_len(S_LEN("ffs"));
 
     // Apply the first entry of 'fileformats' to the initial buffer.