Review: Remove long_u: memfile: Refactor: int -> bool.

Replace int with bool where appropriate.

src/nvim/memfile_defs.h

@@ -2,6 +2,8 @@
 #define NVIM_MEMFILE_DEFS_H
 
 #include <stdint.h>
+#include <stdbool.h>
+
 #include "nvim/types.h"
 
 /// A block number.
@@ -100,7 +102,7 @@ typedef struct memfile {
   blocknr_T mf_neg_count;            /// number of negative blocks numbers
   blocknr_T mf_infile_count;         /// number of pages in the file
   unsigned mf_page_size;             /// number of bytes in a page
-  int mf_dirty;                      /// TRUE if there are dirty blocks
+  bool mf_dirty;                      /// TRUE if there are dirty blocks
 } memfile_T;
 
 #endif // NVIM_MEMFILE_DEFS_H