Prevent name collisions with internal implementation details

The implementation of the linkage attribute inside extern blocks defines
symbols starting with _rust_extern_with_linkage_. If someone tries to
also define this symbol you will get a symbol conflict or even an ICE.
By adding an unpredictable component to the symbol name, this becomes
less of an issue.

Author: bjorn3

src/consts.rs

@@ -6,6 +6,7 @@ use rustc_codegen_ssa::traits::{
     BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
 };
 use rustc_hir::def::DefKind;
+use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::interpret::{
     self, ConstAllocation, ErrorHandled, Scalar as InterpScalar, read_target_uint,
@@ -384,8 +385,8 @@ fn check_and_apply_linkage<'gcc, 'tcx>(
         // linkage and there are no definitions), then
         // `extern_with_linkage_foo` will instead be initialized to
         // zero.
-        let mut real_name = "_rust_extern_with_linkage_".to_string();
-        real_name.push_str(sym);
+        let real_name =
+            format!("_rust_extern_with_linkage_{:016x}_{sym}", cx.tcx.stable_crate_id(LOCAL_CRATE));
         let global2 = cx.define_global(&real_name, gcc_type, is_tls, attrs.link_section);
         // TODO(antoyo): set linkage.
         let value = cx.const_ptrcast(global1.get_address(None), gcc_type);