rustdoc: fix test's saved stdout

Also reword "test-builder-wrapper" argument help.

src/librustdoc/lib.rs

@@ -534,8 +534,8 @@ fn opts() -> Vec<RustcOptGroup> {
             o.optmulti(
                 "",
                 "test-builder-wrapper",
-                "The wrapper program for running rustc",
-                "WRAPPER",
+                "Wrapper program to pass test-builder and arguments",
+                "PATH",
             )
         }),
         unstable("check", |o| o.optflagmulti("", "check", "Run rustdoc checks")),

tests/run-make/issue-88756-default-output/output-default.stdout

@@ -147,6 +147,8 @@ Options:
                         
         --test-builder PATH
                         The rustc-like binary to use as the test builder
+        --test-builder-wrapper PATH
+                        Wrapper program to pass test-builder and arguments
         --check         Run rustdoc checks
         --generate-redirect-map 
                         Generate JSON file at the top level instead of