Auto merge of #3193 - devnexen:bsd_unitstd_lconst_haiku, r=JohnTitor

haiku adding bsd missing constants

Author: bors

src/unix/haiku/mod.rs

@@ -685,6 +685,9 @@ pub const EOF: ::c_int = -1;
 pub const SEEK_SET: ::c_int = 0;
 pub const SEEK_CUR: ::c_int = 1;
 pub const SEEK_END: ::c_int = 2;
+pub const L_SET: ::c_int = SEEK_SET;
+pub const L_INCR: ::c_int = SEEK_CUR;
+pub const L_XTND: ::c_int = SEEK_END;
 pub const _IOFBF: ::c_int = 0;
 pub const _IONBF: ::c_int = 2;
 pub const _IOLBF: ::c_int = 1;