emscripten: use getentropy from libc (#362)

.github/workflows/tests.yml

@@ -78,7 +78,7 @@ jobs:
         with:
           targets: ${{ matrix.target }}
       - name: Install multilib
-        run: sudo apt-get install gcc-multilib
+        run: sudo apt-get update && sudo apt-get install gcc-multilib
       - uses: Swatinem/rust-cache@v2
       - run: cargo test --target=${{ matrix.target }} --features=std
 

src/emscripten.rs

@@ -2,15 +2,10 @@
 use crate::{util_libc::last_os_error, Error};
 use core::mem::MaybeUninit;
 
-// Not yet defined in libc crate.
-extern "C" {
-    fn getentropy(buffer: *mut libc::c_void, length: usize) -> libc::c_int;
-}
-
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     // Emscripten 2.0.5 added getentropy, so we can use it unconditionally.
     // Unlike other getentropy implementations, there is no max buffer length.
-    let ret = unsafe { getentropy(dest.as_mut_ptr() as *mut libc::c_void, dest.len()) };
+    let ret = unsafe { libc::getentropy(dest.as_mut_ptr() as *mut libc::c_void, dest.len()) };
     if ret < 0 {
         return Err(last_os_error());
     }