Silence clang analyzer warnings

[cgzones]

    linux/LinuxProcessTable.c:795:11: warning: File position of the stream might be 'indeterminate' after a failed operation. Can cause undefined behavior [unix.Stream]
      795 |    while (fgets(buffer, sizeof(buffer), fp)) {
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/LinuxProcessTable.c:795:11: warning: Read function called when stream is in EOF state. Function has no effect [unix.Stream]
      795 |    while (fgets(buffer, sizeof(buffer), fp)) {
          |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/LinuxProcessTable.c:840:11: warning: File position of the stream might be 'indeterminate' after a failed operation. Can cause undefined behavior [unix.Stream]
      840 |    while (fgets(linebuf, sizeof(linebuf), file) != NULL) {
          |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/LinuxProcessTable.c:840:11: warning: Read function called when stream is in EOF state. Function has no effect [unix.Stream]
      840 |    while (fgets(linebuf, sizeof(linebuf), file) != NULL) {
          |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    linux/LinuxMachine.c:81:22: warning: The 1st argument to 'openat' is between -99 and -1 but should be a valid file descriptor or AT_FDCWD [unix.StdCLibraryFunctions]
       81 |       int cpuDirFd = openat(dirfd(dir), entry->d_name, O_DIRECTORY | O_PATH | O_NOFOLLOW);
          |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/LinuxMachine.c:501:11: warning: File position of the stream might be 'indeterminate' after a failed operation. Can cause undefined behavior [unix.Stream]
      501 |    while (fgets(buffer, sizeof(buffer), file)) {
          |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/LinuxMachine.c:501:11: warning: Read function called when stream is in EOF state. Function has no effect [unix.Stream]
      501 |    while (fgets(buffer, sizeof(buffer), file)) {
          |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    linux/Platform.c:467:22: warning: File position of the stream might be 'indeterminate' after a failed operation. Can cause undefined behavior [unix.Stream]
      467 |    } while ((bytes = fread(env + size, 1, capacity - size, fp)) > 0);
          |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/Platform.c:467:22: warning: Read function called when stream is in EOF state. Function has no effect [unix.Stream]
      467 |    } while ((bytes = fread(env + size, 1, capacity - size, fp)) > 0);
          |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/Platform.c:585:15: warning: File position of the stream might be 'indeterminate' after a failed operation. Can cause undefined behavior [unix.Stream]
      585 |       total = fscanf(fp, "full avg10=%32lf avg60=%32lf avg300=%32lf total=%*f ", ten, sixty, threehundred);
          |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/Platform.c:585:15: warning: Read function called when stream is in EOF state. Function has no effect [unix.Stream]
      585 |       total = fscanf(fp, "full avg10=%32lf avg60=%32lf avg300=%32lf total=%*f ", ten, sixty, threehundred);
          |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    linux/Platform.c:789:21: warning: The 1st argument to 'openat' is between -99 and -1 but should be a valid file descriptor or AT_FDCWD [unix.StdCLibraryFunctions]
      789 |       int entryFd = openat(dirfd(dir), entryName, O_DIRECTORY | O_PATH);
          |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Split from #1513

[BenBE]

This doesn't yet resolve all of the clang issues (tested with clang-20), but it's a good start. Let's do the remaining issues with #1513 …