cargo inserts an empty path in LD_LIBRARY_PATH

[sfackler]

This causes lookup to check the working directory which is not good.

cc rust-lang/rust#42851

[codyps]

Introduced by "[784d315] set dylib path correctly for target when running cargo test etc" #4006

cc: @mcgoo @alexcrichton

test:

extern crate cargotest;
extern crate hamcrest;

use cargotest::support::{execs, project};
use hamcrest::assert_that;

#[test]
fn build_with_fake_libc_not_loading() {
    let p = project("foo")
        .file("Cargo.toml", r#"
            [package]
            name = "foo"
            version = "0.0.1"
            authors = []
        "#)
        .file("src/main.rs", r#"
            fn main() {}
        "#)
        .file("src/lib.rs", r#" "#)
        .file("libc.so.6", r#""#);

    assert_that(p.cargo_process("build"), execs().with_status(0));
}

[mbrubeck]

#4006 added lines like this:

 search_path.push(self.host_dylib_path.iter().collect());

where search_path is a Vec<PathBuf> and self.host_dylib_path is an Option<PathBuf>. If self.host_dylib_path is set to None then this will push an empty path into the search path. There is a fix for this in #4278.