illumos: Add _CS_PATH constant

Author: LiamSnow

libc-test/semver/illumos.txt

@@ -19,6 +19,7 @@ TFD_CLOEXEC
 TFD_NONBLOCK
 TFD_TIMER_ABSTIME
 TFD_TIMER_CANCEL_ON_SET
+_CS_PATH
 posix_fadvise
 posix_fallocate
 posix_spawn_file_actions_addfchdir_np

src/unix/solarish/illumos.rs

@@ -154,6 +154,8 @@ pub const LOCK_UN: c_int = 8;
 
 pub const _PC_LAST: c_int = 101;
 
+pub const _CS_PATH: c_int = 65;
+
 pub const VSTATUS: usize = 16;
 pub const VERASE2: usize = 17;