Partially revert "Don't cache dep file (#2322)"

This reverts the "main" code changes of commit
c0a0b6e but keeps the added test.

A better fix will work as follows:
- Always store the dep file in the cache
- In non-preprocessor cache mode, which doesn't consider things
  like file name and included file names, so it can confuse cache
  entries with same preprocessed content but different dep files:
  do not restore the dep file. It is not necessary anyway because
  local preprocessing will produce the file.
- In preprocessor cache mode, which uses input file names and
  hashes to distinguish cache entries, but does not run the
  preprocessor:
  *do* restore the dep file.

Author: ahartmetz

src/compiler/gcc.rs

@@ -290,6 +290,7 @@ where
     let mut language_extensions = true; // by default, GCC allows extensions
     let mut split_dwarf = false;
     let mut need_explicit_dep_target = false;
+    let mut dep_path = None;
     enum DepArgumentRequirePath {
         NotNeeded,
         Missing,
@@ -381,8 +382,9 @@ where
                 dep_flag = OsString::from(arg.flag_str().expect("Dep target flag expected"));
                 dep_target = Some(s.clone());
             }
-            Some(DepArgumentPath(_)) => {
+            Some(DepArgumentPath(path)) => {
                 need_explicit_dep_argument_path = DepArgumentRequirePath::Provided;
+                dep_path = Some(path.clone());
             }
             Some(SerializeDiagnostics(path)) => {
                 serialize_diagnostics = Some(path.clone());
@@ -642,6 +644,16 @@ where
         dependency_args.push(Path::new(&output).with_extension("d").into_os_string());
     }
 
+    if let Some(path) = dep_path {
+        outputs.insert(
+            "d",
+            ArtifactDescriptor {
+                path: path.clone(),
+                optional: false,
+            },
+        );
+    }
+
     if let Some(path) = serialize_diagnostics {
         outputs.insert(
             "dia",
@@ -1450,6 +1462,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(ovec!["-MF", "foo.o.d"], dependency_args);
@@ -1543,6 +1562,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(ovec!["-MF", "foo.o.d"], dependency_args);
@@ -1578,6 +1604,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(
@@ -1617,6 +1650,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(
@@ -1857,6 +1897,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(

src/compiler/nvcc.rs

@@ -1809,6 +1809,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(

src/compiler/nvhpc.rs

@@ -352,6 +352,13 @@ mod test {
                     path: "foo.o".into(),
                     optional: false
                 }
+            ),
+            (
+                "d",
+                ArtifactDescriptor {
+                    path: "foo.o.d".into(),
+                    optional: false
+                }
             )
         );
         assert_eq!(