Document aliases for functions like getuid()

Add the autocfg crate as a build dependency, and introduce
has_doc_alias as a conditional compilation symbol.

1 files changed, 7 insertions, 0 deletions

diff --git a/build.rs b/build.rs
new file mode 100644
index 00000000..ad78ab3f
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,7 @@
+fn main() {
+    let cfg = autocfg::new();
+
+    if cfg.probe_rustc_version(1, 52) {
+        autocfg::emit("has_doc_alias");
+    }
+}