Only depend on CFG_VERSION in rustc_interface

this avoids having to rebuild the whole compiler on each commit when
`omit-git-hash = false`.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -806,8 +806,7 @@ pub fn build_compile_unit_di_node<'ll, 'tcx>(
     name_in_debuginfo.push(codegen_unit_name);
 
     debug!("build_compile_unit_di_node: {:?}", name_in_debuginfo);
-    let rustc_producer =
-        format!("rustc version {}", option_env!("CFG_VERSION").expect("CFG_VERSION"),);
+    let rustc_producer = format!("rustc version {}", tcx.sess.cfg_version);
     // FIXME(#41252) Remove "clang LLVM" if we can get GDB and LLVM to play nice.
     let producer = format!("clang LLVM ({})", rustc_producer);