feat(gs/achilles): Implement extern decls, for glibc functions r/2293

Implement extern decls, which codegen to LLVM as forward-declared
functions, and use these as a hook into calling glibc functions.

We can print to the terminal now! The integration tests can test this
now.

Change-Id: I70af4546b417b888ad9fbb18798db240f77f4e71
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2614
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

1 files changed, 12 insertions, 2 deletions

diff --git a/users/glittershark/achilles/src/ast/mod.rs b/users/glittershark/achilles/src/ast/mod.rs
index 3a2261aeda..22d16c9364 100644
--- a/users/glittershark/achilles/src/ast/mod.rs
+++ b/users/glittershark/achilles/src/ast/mod.rs
@@ -265,8 +265,18 @@ impl<'a> Fun<'a> {
 
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Decl<'a> {
-    Fun { name: Ident<'a>, body: Fun<'a> },
-    Ascription { name: Ident<'a>, type_: Type<'a> },
+    Fun {
+        name: Ident<'a>,
+        body: Fun<'a>,
+    },
+    Ascription {
+        name: Ident<'a>,
+        type_: Type<'a>,
+    },
+    Extern {
+        name: Ident<'a>,
+        type_: FunctionType<'a>,
+    },
 }
 
 ////