Rename directories for some crates from syntax_x to rustc_x

`syntax_expand` -> `rustc_expand`
`syntax_pos` -> `rustc_span`
`syntax_ext` -> `rustc_builtin_macros`

src/librustc_expand/lib.rs

@@ -0,0 +1,67 @@
+#![feature(crate_visibility_modifier)]
+#![feature(decl_macro)]
+#![feature(proc_macro_diagnostic)]
+#![feature(proc_macro_internals)]
+#![feature(proc_macro_span)]
+
+extern crate proc_macro as pm;
+
+// A variant of 'try!' that panics on an Err. This is used as a crutch on the
+// way towards a non-panic!-prone parser. It should be used for fatal parsing
+// errors; eventually we plan to convert all code using panictry to just use
+// normal try.
+#[macro_export]
+macro_rules! panictry {
+    ($e:expr) => {{
+        use errors::FatalError;
+        use std::result::Result::{Err, Ok};
+        match $e {
+            Ok(e) => e,
+            Err(mut e) => {
+                e.emit();
+                FatalError.raise()
+            }
+        }
+    }};
+}
+
+mod placeholders;
+mod proc_macro_server;
+
+pub use mbe::macro_rules::compile_declarative_macro;
+crate use syntax_pos::hygiene;
+pub mod base;
+pub mod build;
+pub mod expand;
+pub use rustc_parse::config;
+pub mod proc_macro;
+
+crate mod mbe;
+
+// HACK(Centril, #64197): These shouldn't really be here.
+// Rather, they should be with their respective modules which are defined in other crates.
+// However, since for now constructing a `ParseSess` sorta requires `config` from this crate,
+// these tests will need to live here in the iterim.
+
+#[cfg(test)]
+mod tests;
+#[cfg(test)]
+mod parse {
+    #[cfg(test)]
+    mod tests;
+    #[cfg(test)]
+    mod lexer {
+        #[cfg(test)]
+        mod tests;
+    }
+}
+#[cfg(test)]
+mod tokenstream {
+    #[cfg(test)]
+    mod tests;
+}
+#[cfg(test)]
+mod mut_visit {
+    #[cfg(test)]
+    mod tests;
+}