Move the wasmtime crate directories form lib/* to wasmtime-*.

This follows a similar change to Cranelift made here:

https://github.com/CraneStation/cranelift/pull/660

wasmtime-obj/src/module.rs

@@ -0,0 +1,69 @@
+use crate::context::layout_vmcontext;
+use crate::data_segment::{declare_data_segment, emit_data_segment};
+use crate::function::{declare_functions, emit_functions};
+use crate::table::{declare_table, emit_table};
+use cranelift_codegen::isa::TargetFrontendConfig;
+use faerie::{Artifact, Decl, Link};
+use wasmtime_environ::{Compilation, DataInitializer, Module, Relocations};
+
+fn emit_vmcontext_init(
+    obj: &mut Artifact,
+    module: &Module,
+    target_config: &TargetFrontendConfig,
+) -> Result<(), String> {
+    let (data, table_relocs) = layout_vmcontext(module, target_config);
+    obj.declare_with(
+        "_vmcontext_init",
+        Decl::Data {
+            writable: false,
+            global: true,
+        },
+        data.to_vec(),
+    )
+    .map_err(|err| format!("{}", err))?;
+    for reloc in table_relocs.iter() {
+        let target_name = format!("_table_{}", reloc.index);
+        obj.link(Link {
+            from: "_vmcontext_init",
+            to: &target_name,
+            at: reloc.offset as u64,
+        })
+        .map_err(|err| format!("{}", err))?;
+    }
+    Ok(())
+}
+
+/// Emits a module that has been emitted with the `wasmtime-environ` environment
+/// implementation to a native object file.
+pub fn emit_module(
+    obj: &mut Artifact,
+    module: &Module,
+    compilation: &Compilation,
+    relocations: &Relocations,
+    data_initializers: &[DataInitializer],
+    target_config: &TargetFrontendConfig,
+) -> Result<(), String> {
+    declare_functions(obj, module, relocations)?;
+
+    for i in 0..data_initializers.len() {
+        declare_data_segment(obj, &data_initializers[i], i)?;
+    }
+
+    for i in 0..module.table_plans.len() {
+        declare_table(obj, i)?;
+    }
+
+    emit_functions(obj, module, compilation, relocations)?;
+
+    for i in 0..data_initializers.len() {
+        emit_data_segment(obj, &data_initializers[i], i)?;
+    }
+
+    for i in 0..module.table_plans.len() {
+        emit_table(obj, i)?;
+    }
+
+    emit_vmcontext_init(obj, module, target_config)?;
+
+    Ok(())
+}