Add cross-language LLVM CFI support to the Rust compiler

This commit adds cross-language LLVM Control Flow Integrity (CFI)
support to the Rust compiler by adding the
`-Zsanitizer-cfi-normalize-integers` option to be used with Clang
`-fsanitize-cfi-icall-normalize-integers` for normalizing integer types
(see https://reviews.llvm.org/D139395).

It provides forward-edge control flow protection for C or C++ and Rust
-compiled code "mixed binaries" (i.e., for when C or C++ and Rust
-compiled code share the same virtual address space). For more
information about LLVM CFI and cross-language LLVM CFI support for the
Rust compiler, see design document in the tracking issue #89653.

Cross-language LLVM CFI can be enabled with -Zsanitizer=cfi and
-Zsanitizer-cfi-normalize-integers, and requires proper (i.e.,
non-rustc) LTO (i.e., -Clinker-plugin-lto).

compiler/rustc_middle/src/ty/sty.rs

@@ -2400,6 +2400,13 @@ impl<'tcx> Ty<'tcx> {
             _ => None,
         }
     }
+
+    pub fn is_c_void(self, tcx: TyCtxt<'_>) -> bool {
+        match self.kind() {
+            ty::Adt(adt, _) => tcx.lang_items().get(LangItem::CVoid) == Some(adt.did()),
+            _ => false,
+        }
+    }
 }
 
 /// Extra information about why we ended up with a particular variance.