Fix rust-langGH-4449: adding strftime* for illumos.

[ref](https://smartos.org/man/3C/strftime)

Author: devnexen

libc-test/semver/illumos.txt

@@ -26,6 +26,8 @@ pthread_attr_get_np
 pthread_attr_getstackaddr
 pthread_attr_setstack
 ptsname_r
+strftime
+strftime_l
 syncfs
 timerfd_create
 timerfd_gettime

src/unix/solarish/illumos.rs

@@ -368,4 +368,18 @@ extern "C" {
         new_value: *const crate::itimerspec,
         old_value: *mut crate::itimerspec,
     ) -> c_int;
+
+    pub fn strftime(
+        s: *mut c_char,
+        maxsize: size_t,
+        format: *const c_char,
+        timeptr: *const crate::tm,
+    ) -> size_t;
+    pub fn strftime_l(
+        s: *mut c_char,
+        maxsize: size_t,
+        format: *const c_char,
+        timeptr: *const crate::tm,
+        loc: crate::locale_t,
+    ) -> size_t;
 }