Conform to Cargo's conventional file layout

Move `src/*.rs` to `src/bin/*.rs` which are automatically inferred as
binaries and move `src/utils.rs` to `src/lib.rs` which is compiled as a
reusable library for each of the binaries we're building.

src/bin/wasm2obj.rs

@@ -56,10 +56,6 @@ use wasmtime_environ::{
 };
 use wasmtime_obj::emit_module;
 
-mod utils;
-
-static LOG_FILENAME_PREFIX: &str = "wasm2obj.dbg.";
-
 const USAGE: &str = "
 Wasm to native object translation utility.
 Takes a binary WebAssembly module into a native object file.
@@ -112,7 +108,7 @@ fn main() {
     if args.flag_debug {
         pretty_env_logger::init();
     } else {
-        utils::init_file_per_thread_logger();
+        wasmtime::init_file_per_thread_logger("wasm2obj.dbg.");
     }
 
     cache_conf::init(args.flag_cache);

src/bin/wasmtime.rs

@@ -54,10 +54,6 @@ use wasmtime_wast::instantiate_spectest;
 #[cfg(feature = "wasi-c")]
 use wasmtime_wasi_c::instantiate_wasi_c;
 
-mod utils;
-
-static LOG_FILENAME_PREFIX: &str = "wasmtime.dbg.";
-
 const USAGE: &str = "
 Wasm runner.
 
@@ -207,7 +203,7 @@ fn main() {
     if args.flag_debug {
         pretty_env_logger::init();
     } else {
-        utils::init_file_per_thread_logger();
+        wasmtime::init_file_per_thread_logger("wasmtime.dbg.");
     }
 
     cache_conf::init(args.flag_cache);

src/bin/wast.rs

@@ -37,10 +37,6 @@ use wasmtime_environ::cache_conf;
 use wasmtime_jit::{Compiler, Features};
 use wasmtime_wast::WastContext;
 
-mod utils;
-
-static LOG_FILENAME_PREFIX: &str = "cranelift.dbg.";
-
 const USAGE: &str = "
 Wast test runner.
 
@@ -80,7 +76,7 @@ fn main() {
     if args.flag_debug {
         pretty_env_logger::init();
     } else {
-        utils::init_file_per_thread_logger();
+        wasmtime::init_file_per_thread_logger("cranelift.dbg.");
     }
 
     cache_conf::init(args.flag_cache);

src/lib.rs

@@ -1,14 +1,12 @@
-pub fn init_file_per_thread_logger() {
-    use super::LOG_FILENAME_PREFIX;
-
-    file_per_thread_logger::initialize(LOG_FILENAME_PREFIX);
+pub fn init_file_per_thread_logger(prefix: &'static str) {
+    file_per_thread_logger::initialize(prefix);
 
     // Extending behavior of default spawner:
     // https://docs.rs/rayon/1.1.0/rayon/struct.ThreadPoolBuilder.html#method.spawn_handler
     // Source code says DefaultSpawner is implementation detail and
     // shouldn't be used directly.
     rayon::ThreadPoolBuilder::new()
-        .spawn_handler(|thread| {
+        .spawn_handler(move |thread| {
             let mut b = std::thread::Builder::new();
             if let Some(name) = thread.name() {
                 b = b.name(name.to_owned());
@@ -16,8 +14,8 @@ pub fn init_file_per_thread_logger() {
             if let Some(stack_size) = thread.stack_size() {
                 b = b.stack_size(stack_size);
             }
-            b.spawn(|| {
-                file_per_thread_logger::initialize(LOG_FILENAME_PREFIX);
+            b.spawn(move || {
+                file_per_thread_logger::initialize(prefix);
                 thread.run()
             })?;
             Ok(())