Use libc's syscall() and NR_GETENTROPY const

Author: mmcco

src/libstd/rand/os.rs

@@ -204,12 +204,6 @@ mod imp {
         _dummy: (),
     }
 
-    extern "C" {
-        fn syscall(number: c_long, ...) -> c_long;
-    }
-
-    const NR_GETENTROPY: c_long = 7;
-
     impl OsRng {
         /// Create a new `OsRng`.
         pub fn new() -> io::Result<OsRng> {
@@ -232,7 +226,7 @@ mod imp {
             // getentropy(2) permits a maximum buffer size of 256 bytes
             for s in v.chunks_mut(256) {
                 let ret = unsafe {
-                    syscall(NR_GETENTROPY, s.as_mut_ptr(), s.len())
+                    libc::syscall(libc::NR_GETENTROPY, s.as_mut_ptr(), s.len())
                 };
                 if ret == -1 {
                     panic!("unexpected getentropy error: {}", errno());