Write .debug_frame information (#53)

* Write .debug_frame information

* mv map_reg

crates/environ/src/frame_layout.rs

@@ -0,0 +1,21 @@
+use cranelift_codegen::isa::CallConv;
+use cranelift_entity::PrimaryMap;
+use cranelift_wasm::DefinedFuncIndex;
+use serde::{Deserialize, Serialize};
+
+pub use cranelift_codegen::ir::FrameLayoutChange;
+
+/// Frame layout information: call convention and
+/// registers save/restore commands.
+#[derive(Serialize, Deserialize, Debug, PartialEq, Eq)]
+pub struct FrameLayout {
+    /// Call convention.
+    pub call_conv: CallConv,
+    /// Frame default/initial commands.
+    pub initial_commands: Box<[FrameLayoutChange]>,
+    /// Frame commands at specific offset.
+    pub commands: Box<[(usize, FrameLayoutChange)]>,
+}
+
+/// Functions frame layouts.
+pub type FrameLayouts = PrimaryMap<DefinedFuncIndex, FrameLayout>;