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

@@ -7,6 +7,17 @@ IP_PKTINFO
 IP_TOS
 IP_TTL
 PIPE_BUF
+SIGEV_PORT
+aio_cancel
+aio_error
+aio_fsync
+aio_read
+aio_result_t
+aio_return
+aio_suspend
+aio_waitn
+aio_write
+aiocb
 bind
 in6_pktinfo
 in_pktinfo

src/unix/solarish/mod.rs

@@ -3048,6 +3048,10 @@ 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")]