illumos gate

Build error with gcc 11:

    tail.c:89:17: error: this 'if' clause does not guard... [-Werror=misleading-indentation]
       89 |                 if (off)                                                \
          |                 ^~
    tail.c:111:25: note: in expansion of macro 'ARG'
      111 |                         ARG(512, FBYTES, RBYTES);
          |                         ^~~
    tail.c:91:25: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
       91 |                         style = (forward);                              \
          |                         ^~~~~
    tail.c:111:25: note: in expansion of macro 'ARG'
      111 |                         ARG(512, FBYTES, RBYTES);
          |                         ^~~
    tail.c:89:17: error: this 'if' clause does not guard... [-Werror=misleading-indentation]
       89 |                 if (off)                                                \
          |                 ^~
    tail.c:114:25: note: in expansion of macro 'ARG'
      114 |                         ARG(1, FBYTES, RBYTES);
          |                         ^~~
    tail.c:91:25: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
       91 |                         style = (forward);                              \
          |                         ^~~~~
    tail.c:114:25: note: in expansion of macro 'ARG'
      114 |                         ARG(1, FBYTES, RBYTES);
          |                         ^~~
    tail.c:89:17: error: this 'if' clause does not guard... [-Werror=misleading-indentation]
       89 |                 if (off)                                                \
          |                 ^~
    tail.c:120:25: note: in expansion of macro 'ARG'
      120 |                         ARG(1, FLINES, RLINES);
          |                         ^~~
    tail.c:91:25: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
       91 |                         style = (forward);                              \
          |                         ^~~~~
    tail.c:120:25: note: in expansion of macro 'ARG'
      120 |                         ARG(1, FLINES, RLINES);
          |                         ^~~
    cc1: all warnings being treated as errors

The argument with ncb options can have prefix '+' or '', denoting if the starting location should be relative to beginning of the file (), or end of the file (-, default), therefore the case '' should always set style = (forward);