rustdoc: forward -Z options to rustc

Currently rustdoc does not forward `-Z` options to rustc when building
test executables. This makes impossible to use rustdoc to run test
samples when crate under test is instrumented with one of sanitizers
`-Zsanitizer=...`, since the final linking step will not include
sanitizer runtime library.

Forward `-Z` options to rustc to solve the issue.

Helps with #43031.

src/librustdoc/test.rs

@@ -279,6 +279,9 @@ fn run_test(
     for codegen_options_str in &options.codegen_options_strs {
         compiler.arg("-C").arg(&codegen_options_str);
     }
+    for debugging_option_str in &options.debugging_options_strs {
+        compiler.arg("-Z").arg(&debugging_option_str);
+    }
     if no_run {
         compiler.arg("--emit=metadata");
     }