Importing from rustpkg in pkg.rs causes link error

[dcolish]

When trying to convert rust-http-client to use rustpkg I ran into some issues during link phase. With a custom pkg.rs, I am able to cause the following output:

WARNING: The Rust package manager is experimental and may be unstable
rust: ~"Using sysroot: Some(@{is_absolute: true, components: ~[~\"home\", ~\"dcolish\", ~\"local\", ~\"rust\", ~
rust: ~"whole = rust-http-client part = rust-http-client"
rust: ~"rust-http-client doesn\'t look like an explicit-version thing"
rust: ~"rust-http-client has no explicit version"
rust: ~"try_getting_version: rust-http-client"
rust: ~"local_path = rust_http_client, remote_path = rust-http-client"
rust: ~"=> p = whatever.rs"
rust: ~"=> p = .git"
rust: ~"p = .git, remote_path = rust-http-client"
rust: ~"whole = .git part = .git"
rust: ~".git doesn\'t look like an explicit-version thing"
rust: ~"=> p = .gitignore"
rust: ~"=> p = rust-http-client"
rust: ~"p = rust-http-client, remote_path = rust-http-client"
rust: ~"build: workspace = . pkgid = rust_http_client-0.1"
rust: ~"Destination dir = ./build/rust_http_client"
rust: ~"Package src = {root: {is_absolute: false, components: ~[~\".\"]}, dst_dir: {is_absolute: false, componen
rust: ~"Package source directory = Some({is_absolute: false, components: ~[~\".\", ~\"src\", ~\"rust-http-client
rust: ~"Returning package script with id &{remote_path: {__field__: {is_absolute: false, components: ~[~\"rust-h
rust: ~"run_custom: post_build"
rust: ~"Working directory = ./build/rust_http_client"
rust: ~"Building output filenames with script name ./src/rust-http-client/pkg.rs"
rust: ~"Root is /home/dcolish/local, calling compile_rest"
rust: ~"Calling build_output_filenames with ./build/rust_http_client, building library? @false"
rust: ~"Outputs are @{out_filename: {is_absolute: false, components: ~[~\".\", ~\"build\", ~\"rust_http_client\"
rust: ~"\"additional libraries:\""
./src/rust-http-client/pkg.rs:2:4: 2:12 warning: unused import [-W unused-imports (default)]
./src/rust-http-client/pkg.rs:2 use std::run;
                                    ^~~~~~~~
error: linking with `cc` failed with code 1
note: cc arguments: -L/home/dcolish/local/rust/trunk/lib/rustc/x86_64-unknown-linux-gnu/lib -m64 -o ./build/rust
note: /usr/bin/ld: cannot find -lrustllvm
collect2: error: ld returned 1 exit status

error: aborting due to previous error
rust: task failed at 'explicit failure', /home/dcolish/workspace/rust/src/libsyntax/diagnostic.rs:98
rust: domain main @0x1b70c80 root task failed

The smallest program that I can write to cause this behavior is the following

$ cat pkg.rs
extern mod rustpkg;
fn main() {}

[dcolish]

Tracked the call path to here https://github.com/mozilla/rust/blob/master/src/librustpkg/util.rs#L287

[catamorphism]

Related to #6401

[catamorphism]

#7403 should fix this when it lands.

[catamorphism]

Testing this.