Auto merge of #2072 - smklein:solarish_directory, r=Amanieu

Add O_DIRECTORY to solarish

FYI `@pfmooney` . I was trying to port [nix](https://crates.io/crates/nix) to illumos, and noticed this in the illumos-gate [headers](https://github.com/illumos/illumos-gate/blob/221e47fb90c5fcfe7add9a33f6c915ee5253ece9/usr/src/uts/common/sys/fcntl.h), but not in libc.

src/unix/solarish/mod.rs

@@ -994,6 +994,7 @@ pub const O_EXCL: ::c_int = 1024;
 pub const O_NOCTTY: ::c_int = 2048;
 pub const O_TRUNC: ::c_int = 512;
 pub const O_NOFOLLOW: ::c_int = 0x20000;
+pub const O_DIRECTORY: ::c_int = 0x1000000;
 pub const O_SEARCH: ::c_int = 0x200000;
 pub const O_EXEC: ::c_int = 0x400000;
 pub const O_CLOEXEC: ::c_int = 0x800000;