Attempt to fix the run_with_library_paths test for Windows.

I was just pasting the build directories into Rust string literals, so Windows
paths with backslashes were being interpreted as having unknown string
escapes. Raw string guards should fix this for all but the most pathological
of build directories.

tests/run.rs

@@ -602,7 +602,7 @@ fn run_with_library_paths() {
     // Only link search directories within the target output directory are
     // propagated through to dylib_path_envvar() (see #3366).
     let mut dir1 = p.target_debug_dir();
-    dir1.push("foo");
+    dir1.push("foo\\backslash");
 
     let mut dir2 = p.target_debug_dir();
     dir2.push("dir=containing=equal=signs");
@@ -614,20 +614,20 @@ fn run_with_library_paths() {
             authors = []
             build = "build.rs"
         "#)
-        .file("build.rs", &format!(r#"
+        .file("build.rs", &format!(r##"
             fn main() {{
-                println!("cargo:rustc-link-search=native={}");
-                println!("cargo:rustc-link-search={}");
+                println!(r#"cargo:rustc-link-search=native={}"#);
+                println!(r#"cargo:rustc-link-search={}"#);
             }}
-        "#, dir1.display(), dir2.display()))
-        .file("src/main.rs", &format!(r#"
+        "##, dir1.display(), dir2.display()))
+        .file("src/main.rs", &format!(r##"
             fn main() {{
                 let search_path = std::env::var_os("{}").unwrap();
                 let paths = std::env::split_paths(&search_path).collect::<Vec<_>>();
-                assert!(paths.contains(&"{}".into()));
-                assert!(paths.contains(&"{}".into()));
+                assert!(paths.contains(&r#"{}"#.into()));
+                assert!(paths.contains(&r#"{}"#.into()));
             }}
-        "#, dylib_path_envvar(), dir1.display(), dir2.display()));
+        "##, dylib_path_envvar(), dir1.display(), dir2.display()));
 
     assert_that(p.cargo_process("run"), execs().with_status(0));
 }