Remove long_u: Passing-by: put_time(): Refactor implementation.

put_time() had a complicated implementation, because of having to shift
an 8-byte value in a portable way with old means.
That can be greatly simplified now, using a C99 fixed-size type.

src/nvim/misc2.c

@@ -511,34 +511,12 @@ int put_bytes(FILE *fd, uintmax_t number, unsigned int len)
   return OK;
 }
 
-
-/*
- * Write time_t to file "fd" in 8 bytes.
- */
-void put_time(FILE *fd, time_t the_time)
+/// Write time_t to file "fd" in 8 bytes.
+void put_time(FILE *fd, time_t time_)
 {
-  int c;
-  int i;
-  time_t wtime = the_time;
-
-  /* time_t can be up to 8 bytes in size, more than long_u, thus we
-   * can't use put_bytes() here.
-   * Another problem is that ">>" may do an arithmetic shift that keeps the
-   * sign.  This happens for large values of wtime.  A cast to long_u may
-   * truncate if time_t is 8 bytes.  So only use a cast when it is 4 bytes,
-   * it's safe to assume that long_u is 4 bytes or more and when using 8
-   * bytes the top bit won't be set. */
-  for (i = 7; i >= 0; --i) {
-    if (i + 1 > (int)sizeof(time_t))
-      /* ">>" doesn't work well when shifting more bits than avail */
-      putc(0, fd);
-    else {
-#if defined(SIZEOF_TIME_T) && SIZEOF_TIME_T > 4
-      c = (int)(wtime >> (i * 8));
-#else
-      c = (int)((long_u)wtime >> (i * 8));
-#endif
-      putc(c, fd);
-    }
+  // time_t can be up to 8 bytes in size, more than uintmax_t in 32 bits
+  // systems, thus we can't use put_bytes() here.
+  for (unsigned int i = 7; i < 8; --i) {
+    putc((int)((uint64_t)time_ >> (i * 8)), fd);
   }
 }