Open files that are CRC'd whole with FREQUENT_ACCESS

ac368f4 taught intfstream_crc_step() to fold the checksum straight
out of the VFS's mapping when the file was opened with
RETRO_VFS_FILE_ACCESS_HINT_FREQUENT_ACCESS, and bade0b7 moved the
content scanner onto it.  The other places that open a file only to
hash all of it were still HINT_NONE: the core updater's sliced CRC
of the installed core, the core backup and restore CRCs of the
backup file, and netplay's CRC of the content at session start.
Same hint at all four; where the VFS cannot map (a URL scheme, a
huge file on a 32-bit host) it is a hint and the read path is what
it was.

Compiled through the real build rule; core_crc_slice_test and
core_backup_io_test pass under ASan.

core_backup.c

@@ -269,7 +269,7 @@ bool core_backup_get_backup_crc(char *s, uint32_t *crc)
             /* Open backup file */
             backup_file = intfstream_open_file(
                   s, RETRO_VFS_FILE_ACCESS_READ,
-                  RETRO_VFS_FILE_ACCESS_HINT_NONE);
+                  RETRO_VFS_FILE_ACCESS_HINT_FREQUENT_ACCESS);
 
             if (backup_file)
             {

network/netplay/netplay_frontend.c

@@ -285,8 +285,12 @@ uint32_t netplay_content_crc(void)
       }
       else
       {
+         /* The whole content file, hashed once at session start:
+          * FREQUENT_ACCESS so the VFS maps it where it can and the
+          * CRC is folded from the mapping rather than read out. */
          intfstream_t *fd = intfstream_open_file(path,
-               RETRO_VFS_FILE_ACCESS_READ, RETRO_VFS_FILE_ACCESS_HINT_NONE);
+               RETRO_VFS_FILE_ACCESS_READ,
+               RETRO_VFS_FILE_ACCESS_HINT_FREQUENT_ACCESS);
          if (fd)
          {
             if (!intfstream_get_crc(fd, &crc))

tasks/task_core_backup.c

@@ -938,7 +938,7 @@ static void task_core_restore_handler(retro_task_t *task)
                if (!(backup_handle->backup_file = intfstream_open_file(
                            backup_handle->backup_path,
                            RETRO_VFS_FILE_ACCESS_READ,
-                           RETRO_VFS_FILE_ACCESS_HINT_NONE)))
+                           RETRO_VFS_FILE_ACCESS_HINT_FREQUENT_ACCESS)))
                {
                   RARCH_ERR("[Core Restore] Failed to determine CRC of core backup file: \"%s\".\n",
                         backup_handle->backup_path);

tasks/task_core_updater.c

@@ -263,9 +263,11 @@ static bool task_core_updater_crc_step(core_crc_slice_t *slice,
    if (!slice->active)
    {
       slice->accumulator = 0;
+      /* FREQUENT_ACCESS: mapped where the VFS can, and each
+       * crc_step() then folds from the mapping without a read. */
       if (!(slice->file = intfstream_open_file(core_path,
                   RETRO_VFS_FILE_ACCESS_READ,
-                  RETRO_VFS_FILE_ACCESS_HINT_NONE)))
+                  RETRO_VFS_FILE_ACCESS_HINT_FREQUENT_ACCESS)))
       {
          *crc = 0;
          return true;