Add getrandom() bindings on linux and android

Closes #659

Author: josephlr

src/unix/linux_like/android/mod.rs

@@ -2195,6 +2195,11 @@ extern {
     pub fn inotify_add_watch(fd: ::c_int,
                              path: *const ::c_char,
                              mask: u32) -> ::c_int;
+    pub fn getrandom(
+        buf: *mut u8,
+        buflen: ::size_t,
+        flags: ::c_uint,
+    ) -> ::ssize_t;
 }
 
 cfg_if! {

src/unix/linux_like/linux/mod.rs

@@ -2666,6 +2666,11 @@ extern {
     pub fn inotify_add_watch(fd: ::c_int,
                              path: *const ::c_char,
                              mask: u32) -> ::c_int;
+    pub fn getrandom(
+        buf: *mut u8,
+        buflen: ::size_t,
+        flags: ::c_uint,
+    ) -> ::ssize_t;
 }
 
 cfg_if! {