Don't generate DWARF sections when no functions were compiled. (#894)

crates/environ/src/address_map.rs

@@ -48,10 +48,22 @@ pub type ValueLabelsRanges = PrimaryMap<DefinedFuncIndex, cranelift_codegen::Val
 /// Stack slots for functions.
 pub type StackSlots = PrimaryMap<DefinedFuncIndex, ir::StackSlots>;
 
+/// Memory definition offset in the VMContext structure.
+#[derive(Debug, Clone)]
+pub enum ModuleMemoryOffset {
+    /// Not available.
+    None,
+    /// Offset to the defined memory.
+    Defined(u32),
+    /// Offset to the imported memory.
+    Imported(u32),
+}
+
 /// Module `vmctx` related info.
+#[derive(Debug, Clone)]
 pub struct ModuleVmctxInfo {
     /// The memory definition offset in the VMContext structure.
-    pub memory_offset: i64,
+    pub memory_offset: ModuleMemoryOffset,
 
     /// The functions stack slots.
     pub stack_slots: StackSlots,