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/errors.rs

@@ -111,8 +111,24 @@ pub struct CannotMixAndMatchSanitizers {
 pub struct CannotEnableCrtStaticLinux;
 
 #[derive(Diagnostic)]
-#[diag(session_sanitizer_cfi_enabled)]
-pub struct SanitizerCfiEnabled;
+#[diag(session_sanitizer_cfi_requires_lto)]
+pub struct SanitizerCfiRequiresLto;
+
+#[derive(Diagnostic)]
+#[diag(session_sanitizer_cfi_canonical_jump_tables_requires_cfi)]
+pub struct SanitizerCfiCanonicalJumpTablesRequiresCfi;
+
+#[derive(Diagnostic)]
+#[diag(session_sanitizer_cfi_generalize_pointers_requires_cfi)]
+pub struct SanitizerCfiGeneralizePointersRequiresCfi;
+
+#[derive(Diagnostic)]
+#[diag(session_sanitizer_cfi_normalize_integers_requires_cfi)]
+pub struct SanitizerCfiNormalizeIntegersRequiresCfi;
+
+#[derive(Diagnostic)]
+#[diag(session_split_lto_unit_requires_lto)]
+pub struct SplitLtoUnitRequiresLto;
 
 #[derive(Diagnostic)]
 #[diag(session_unstable_virtual_function_elimination)]