adding arc4random* api family for solarish.

[solaris](https://docs.oracle.com/cd/E88353_01/html/E37843/arc4random-buf-3c.html)
[illumos](https://illumos.org/man/3C/arc4random_buf)

(backport <#3944>)
(cherry picked from commit 71f74cd)

Author: devnexen

libc-test/semver/solarish.txt

@@ -26,6 +26,9 @@ aio_suspend
 aio_waitn
 aio_write
 aiocb
+arc4random
+arc4random_buf
+arc4random_uniform
 bind
 in6_pktinfo
 in_pktinfo

src/unix/solarish/mod.rs

@@ -3087,6 +3087,10 @@ extern "C" {
     pub fn __major(version: ::c_int, devnum: ::dev_t) -> ::major_t;
     pub fn __minor(version: ::c_int, devnum: ::dev_t) -> ::minor_t;
     pub fn __makedev(version: ::c_int, majdev: ::major_t, mindev: ::minor_t) -> ::dev_t;
+
+    pub fn arc4random() -> u32;
+    pub fn arc4random_buf(buf: *mut ::c_void, nbytes: ::size_t);
+    pub fn arc4random_uniform(upper_bound: u32) -> u32;
 }
 
 #[link(name = "sendfile")]