Fallback to other times if fetching file create time fails.

On Travis, fetching file creation time fails. Because codegen tests
depended on being able to retrieve this time, the tests themselves would
fail. Instead of failing outright, this commit makes an effort to find
_some_ time to associate with a file's creation, even if the time is
suboptimal.

codegen/tests/compiletest.rs

@@ -1,7 +1,7 @@
 extern crate compiletest_rs as compiletest;
 
-use std::io;
 use std::path::{Path, PathBuf};
+use std::{io, fs::Metadata, time::SystemTime};
 
 #[derive(Copy, Clone)]
 enum Kind {
@@ -43,20 +43,31 @@ fn link_flag(flag: &str, lib: &str, rel_path: &[&str]) -> String {
     format!("{} {}={}", flag, lib, path.display())
 }
 
+fn best_time_for(metadata: &Metadata) -> SystemTime {
+    metadata.created()
+        .or_else(|_| metadata.modified())
+        .or_else(|_| metadata.accessed())
+        .unwrap_or_else(|_| SystemTime::now())
+}
+
 fn extern_dep(name: &str, kind: Kind) -> io::Result<String> {
     let deps_root = target_path().join("deps");
     let dep_name = format!("{}{}", kind.prefix(), name);
 
     let mut dep_path: Option<PathBuf> = None;
     for entry in deps_root.read_dir().expect("read_dir call failed") {
-        let entry = entry?;
+        let entry = match entry {
+            Ok(entry) => entry,
+            Err(_) => continue
+        };
+
         let filename = entry.file_name();
         let filename = filename.to_string_lossy();
         let lib_name = filename.split('.').next().unwrap().split('-').next().unwrap();
 
         if lib_name == dep_name && filename.ends_with(kind.extension()) {
             if let Some(ref mut existing) = dep_path {
-                if entry.metadata()?.created()? > existing.metadata()?.created()? {
+                if best_time_for(&entry.metadata()?) > best_time_for(&existing.metadata()?) {
                     *existing = entry.path().into();
                 }
             } else {