Add --all flag to ./x.py clean

This flag removes all build artifacts, including the LLVM build
directory.

src/bootstrap/builder.rs

@@ -306,7 +306,7 @@ impl<'a> Builder<'a> {
             Subcommand::Bench { ref paths, .. } => (Kind::Bench, &paths[..]),
             Subcommand::Dist { ref paths } => (Kind::Dist, &paths[..]),
             Subcommand::Install { ref paths } => (Kind::Install, &paths[..]),
-            Subcommand::Clean => panic!(),
+            Subcommand::Clean { .. } => panic!(),
         };
 
         let builder = Builder {

src/bootstrap/clean.rs

@@ -13,7 +13,7 @@
 //! Responsible for cleaning out a build directory of all old and stale
 //! artifacts to prepare for a fresh build. Currently doesn't remove the
 //! `build/cache` directory (download cache) or the `build/$target/llvm`
-//! directory as we want that cached between builds.
+//! directory unless the --all flag is present.
 
 use std::fs;
 use std::io::{self, ErrorKind};
@@ -21,8 +21,12 @@ use std::path::Path;
 
 use Build;
 
-pub fn clean(build: &Build) {
+pub fn clean(build: &Build, all: bool) {
     rm_rf("tmp".as_ref());
+
+    if all {
+        rm_rf(&build.out);
+    } else {
         rm_rf(&build.out.join("tmp"));
         rm_rf(&build.out.join("dist"));
 
@@ -41,6 +45,7 @@ pub fn clean(build: &Build) {
                 rm_rf(&path);
             }
         }
+    }
 }
 
 fn rm_rf(path: &Path) {

src/bootstrap/flags.rs

@@ -60,7 +60,9 @@ pub enum Subcommand {
         paths: Vec<PathBuf>,
         test_args: Vec<String>,
     },
-    Clean,
+    Clean {
+        all: bool,
+    },
     Dist {
         paths: Vec<PathBuf>,
     },
@@ -147,6 +149,7 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`");
                 opts.optmulti("", "test-args", "extra arguments", "ARGS");
             },
             "bench" => { opts.optmulti("", "test-args", "extra arguments", "ARGS"); },
+            "clean" => { opts.optflag("", "all", "clean all build artifacts"); },
             _ => { },
         };
 
@@ -293,7 +296,10 @@ Arguments:
                     println!("\nclean takes no arguments\n");
                     usage(1, &opts, &subcommand_help, &extra_help);
                 }
-                Subcommand::Clean
+
+                Subcommand::Clean {
+                    all: matches.opt_present("all"),
+                }
             }
             "dist" => {
                 Subcommand::Dist {

src/bootstrap/lib.rs

@@ -345,8 +345,8 @@ impl Build {
             job::setup(self);
         }
 
-        if let Subcommand::Clean = self.config.cmd {
+        if let Subcommand::Clean { all } = self.config.cmd {
-            return clean::clean(self);
+            return clean::clean(self, all);
         }
 
         self.verbose("finding compilers");