rustbuild: Use tool_cmd() instead of tool()

This sets up the dynamic loader path for dylibs required, so should fix the MSVC
build right now.

Author: alexcrichton

src/bootstrap/build/check.rs

@@ -8,14 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::process::Command;
-
 use build::{Build, Compiler};
 
 pub fn linkcheck(build: &Build, stage: u32, host: &str) {
     println!("Linkcheck stage{} ({})", stage, host);
     let compiler = Compiler::new(stage, host);
-    let linkchecker = build.tool(&compiler, "linkchecker");
-    build.run(Command::new(&linkchecker)
-                     .arg(build.out.join(host).join("doc")));
+    build.run(build.tool_cmd(&compiler, "linkchecker")
+                   .arg(build.out.join(host).join("doc")));
 }

src/bootstrap/build/doc.rs

@@ -143,7 +143,7 @@ pub fn rustc(build: &Build, stage: u32, host: &str, out: &Path) {
 pub fn error_index(build: &Build, stage: u32, host: &str, out: &Path) {
     println!("Documenting stage{} error index ({})", stage, host);
     let compiler = Compiler::new(stage, host);
-    let mut index = Command::new(build.tool(&compiler, "error_index_generator"));
+    let mut index = build.tool_cmd(&compiler, "error_index_generator");
     index.arg("html");
     index.arg(out.join("error-index.html"));