Rollup merge of rust-lang#49140 - semarie:rustdoc-test-path, r=alexcrichton

Allow test target to pass without installing

explicitly pass -L target-lib to rustdoc

on OpenBSD, without it, it fails on several tests with:
```
error[E0463]: can't find crate for `std`
```

Author: kennytm

src/test/run-make/tools.mk

@@ -9,7 +9,7 @@ RUSTC_ORIGINAL := $(RUSTC)
 BARE_RUSTC := $(HOST_RPATH_ENV) '$(RUSTC)'
 BARE_RUSTDOC := $(HOST_RPATH_ENV) '$(RUSTDOC)'
 RUSTC := $(BARE_RUSTC) --out-dir $(TMPDIR) -L $(TMPDIR) $(RUSTFLAGS)
-RUSTDOC := $(BARE_RUSTDOC)
+RUSTDOC := $(BARE_RUSTDOC) -L $(TARGET_RPATH_DIR)
 ifdef RUSTC_LINKER
 RUSTC := $(RUSTC) -Clinker=$(RUSTC_LINKER)
 RUSTDOC := $(RUSTDOC) --linker $(RUSTC_LINKER) -Z unstable-options

src/tools/compiletest/src/runtest.rs

@@ -1324,6 +1324,8 @@ impl<'test> TestCx<'test> {
         let mut rustdoc = Command::new(rustdoc_path);
 
         rustdoc
+            .arg("-L")
+            .arg(self.config.run_lib_path.to_str().unwrap())
             .arg("-L")
             .arg(aux_dir)
             .arg("-o")