rustdoc: Don't try to load source files from external crates

Local items defined in external macros shouldn't generate rendered source files and should link to the external crate's docs instead.

src/test/rustdoc/auxiliary/external-macro-src.rs

@@ -0,0 +1,15 @@
+// compile-flags:--remap-path-prefix={{src-base}}=/does-not-exist
+
+#![doc(html_root_url = "https://example.com/")]
+
+#[macro_export]
+macro_rules! make_foo {
+    () => {
+        pub struct Foo;
+        impl Foo {
+            pub fn new() -> Foo {
+                Foo
+            }
+        }
+    }
+}

src/test/rustdoc/external-macro-src.rs

@@ -0,0 +1,15 @@
+// aux-build:external-macro-src.rs
+// ignore-tidy-linelength
+
+#![crate_name = "foo"]
+
+#[macro_use]
+extern crate external_macro_src;
+
+// @has foo/index.html '//a[@href="../src/foo/external-macro-src.rs.html#4-15"]' '[src]'
+
+// @has foo/struct.Foo.html
+// @has - '//a[@href="https://example.com/src/external_macro_src/external-macro-src.rs.html#8"]' '[src]'
+// @has - '//a[@href="https://example.com/src/external_macro_src/external-macro-src.rs.html#9-13"]' '[src]'
+// @has - '//a[@href="https://example.com/src/external_macro_src/external-macro-src.rs.html#10-12"]' '[src]'
+make_foo!();

src/test/rustdoc/issue-26606.rs

@@ -7,5 +7,5 @@
 extern crate issue_26606_macro;
 
 // @has issue_26606/constant.FOO.html
-// @has - '//a/@href' '../src/issue_26606/auxiliary/issue-26606-macro.rs.html#3'
+// @has - '//a/@href' '../src/issue_26606_macro/issue-26606-macro.rs.html#3'
 make_item!(FOO);

src/test/rustdoc/thread-local-src.rs

@@ -0,0 +1,6 @@
+#![crate_name = "foo"]
+
+// @has foo/index.html '//a[@href="../src/foo/thread-local-src.rs.html#1-6"]' '[src]'
+
+// @has foo/constant.FOO.html '//a/@href' 'https://doc.rust-lang.org/nightly/src/std/'
+thread_local!(pub static FOO: bool = false);