bootstrap/clean.rs cannot handle symlinks

[nodakai]

The implementation can only handle regular files and directories:

$ RUST_BACKTRACE=1 make clean
extracting /home/nodakai/src/rust-HEAD/build/cache/2017-02-01/rust-std-beta-x86_64-unknown-linux-gnu.tar.gz
extracting /home/nodakai/src/rust-HEAD/build/cache/2017-02-01/rustc-beta-x86_64-unknown-linux-gnu.tar.gz
extracting /home/nodakai/src/rust-HEAD/build/cache/407edef22e894266eb562618cba5ca9757051946/cargo-nightly-x86_64-unknown-linux-gnu.tar.gz
    Finished dev [unoptimized] target(s) in 0.0 secs
thread 'main' panicked at 'failed to remove dir /home/nodakai/src/rust-HEAD/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/doc: Not a directory (os error 20)', src/bootstrap/clean.rs:84
stack backtrace:
   1:     0x55fb07f52d7c - std::sys::imp::backtrace::tracing::imp::write::h23bcdb89e70c5bbf
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:42
   2:     0x55fb07f5b0be - std::panicking::default_hook::{{closure}}::he7b82439fd2d2bb6
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panicking.rs:351
   3:     0x55fb07f5acc4 - std::panicking::default_hook::he1cd4269c1558f23
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panicking.rs:367
   4:     0x55fb07f5b4fb - std::panicking::rust_panic_with_hook::h006b37e36b7c8982
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panicking.rs:555
   5:     0x55fb07f5b344 - std::panicking::begin_panic::h043cddfdd3933cc4
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panicking.rs:517
   6:     0x55fb07f5b2b9 - std::panicking::begin_panic_fmt::h34e588bba6b8a2c2
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panicking.rs:501
   7:     0x55fb07ddf1ab - bootstrap::clean::do_op::hdae2989b2a396018
   8:     0x55fb07ddd187 - bootstrap::clean::rm_rf::h8404e5c7dea5380d
   9:     0x55fb07ddd08c - bootstrap::clean::rm_rf::h8404e5c7dea5380d
  10:     0x55fb07ddd08c - bootstrap::clean::rm_rf::h8404e5c7dea5380d
  11:     0x55fb07ddc4b1 - bootstrap::clean::clean::h735ac6b031a4468a
  12:     0x55fb07e4a82f - bootstrap::Build::build::hec419daa0bd76b14
  13:     0x55fb07cbe3be - bootstrap::main::h8b662183e4af9c72
  14:     0x55fb07f6250a - __rust_maybe_catch_panic
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libpanic_unwind/lib.rs:98
  15:     0x55fb07f5bc66 - std::rt::lang_start::h1ef940195e3c010e
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panicking.rs:436
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/panic.rs:361
                        at /buildslave/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libstd/rt.rs:57
  16:     0x55fb07cbe539 - main
  17:     0x7f27382bf2b0 - __libc_start_main
  18:     0x55fb07cb66a9 - _start
  19:                0x0 - <unknown>
Build completed unsuccessfully in 0:00:02
Makefile:37: recipe for target 'clean' failed
make: *** [clean] Error 101

$ LANG=C ll /home/nodakai/src/rust-HEAD/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/doc
lrwxrwxrwx 1 nodakai nodakai 69 Mar 12 16:11 /home/nodakai/src/rust-HEAD/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/doc -> /home/nodakai/src/rust-HEAD/build/x86_64-unknown-linux-gnu/crate-docs/

Apparently the symlink was generated by

    let my_out = build.crate_doc_out(target);
    build.clear_if_dirty(&my_out, &rustdoc);
    t!(symlink_dir_force(&my_out, &out_dir));

in bootstrap/doc.rs

[CleanCut]

I was able to reproduce this on my setup with:

export MYARCH=x86_64-apple-darwin && mkdir -p build/$MYARCH/subdir && touch build/$MYARCH/subdir/file && ln -s build/$MYARCH/subdir/file build/$MYARCH/subdir/symlink