Fix build for target_os android

Add `target_os = android` to the conditional compilation flags.
Add targets `aarch64-linux-android` and `arm-linux-androideabi` with the
use of `cross` the the GH action.

.github/workflows/memfd.yml

@@ -79,3 +79,25 @@ jobs:
         with:
           command: build
           args: --manifest-path=Cargo.toml
+  cross:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target:
+          - arm-linux-androideabi
+          - aarch64-linux-android
+    steps:
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          target: ${{ matrix.target }}
+          override: true
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Build
+        uses: actions-rs/cargo@v1
+        with:
+          use-cross: true
+          command: build
+          args: --target=${{ matrix.target }} --manifest-path=Cargo.toml

Cargo.toml

@@ -15,7 +15,7 @@ exclude = [
 
 [dependencies]
 # Private dependencies.
-libc = "0.2"
+libc = "^0.2.99"
 
 [package.metadata.release]
 sign-commit = true

src/lib.rs

@@ -36,10 +36,10 @@
     unused,
 )]
 #![cfg_attr(docsrs, feature(doc_cfg))]
-#![cfg_attr(docsrs, doc(cfg(target_os="linux")))]
+#![cfg_attr(docsrs, doc(cfg(any(target_os = "android", target_os= "linux" ))))]
 // No-op crate on platforms that do not support memfd_create, instead of failing to link, or at
 // runtime.
-#![cfg(target_os="linux")]
+#![cfg(any(target_os = "android", target_os= "linux"))]
 
 mod errors;
 mod memfd;

src/memfd.rs

@@ -2,7 +2,7 @@ use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 use std::{ffi, fs, os::raw};
 use crate::{nr, sealing};
 
-#[cfg(target_os="linux")]
+#[cfg(any(target_os = "android", target_os="linux"))]
 unsafe fn memfd_create(name: *const raw::c_char, flags: raw::c_uint) -> raw::c_int {
     libc::syscall(libc::SYS_memfd_create, name, flags) as raw::c_int
 }