Auto merge of #3142 - connor4312:wasi-irwx, r=JohnTitor

add S_IRWX* constants to wasi

It seems like all other platforms have `/S_IRWX[OGU]/`, and the `libc` crate looks for them, but they were missing in WASI.

Author: bors

src/wasi.rs

@@ -246,12 +246,15 @@ pub const S_IFREG: mode_t = 32768;
 pub const S_IFLNK: mode_t = 40960;
 pub const S_IFSOCK: mode_t = 49152;
 pub const S_IFMT: mode_t = 57344;
+pub const S_IRWXO: mode_t = 0x7;
 pub const S_IXOTH: mode_t = 0x1;
 pub const S_IWOTH: mode_t = 0x2;
 pub const S_IROTH: mode_t = 0x4;
+pub const S_IRWXG: mode_t = 0x38;
 pub const S_IXGRP: mode_t = 0x8;
 pub const S_IWGRP: mode_t = 0x10;
 pub const S_IRGRP: mode_t = 0x20;
+pub const S_IRWXU: mode_t = 0x1c0;
 pub const S_IXUSR: mode_t = 0x40;
 pub const S_IWUSR: mode_t = 0x80;
 pub const S_IRUSR: mode_t = 0x100;