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_session/src/config.rs

@@ -1036,6 +1036,14 @@ fn default_configuration(sess: &Session) -> CrateConfig {
         ret.insert((sym::sanitize, Some(symbol)));
     }
 
+    if sess.is_sanitizer_cfi_generalize_pointers_enabled() {
+        ret.insert((sym::sanitizer_cfi_generalize_pointers, None));
+    }
+
+    if sess.is_sanitizer_cfi_normalize_integers_enabled() {
+        ret.insert((sym::sanitizer_cfi_normalize_integers, None));
+    }
+
     if sess.opts.debug_assertions {
         ret.insert((sym::debug_assertions, None));
     }