Add fine-grained LLVM CFI support to the Rust compiler

This commit improves the LLVM Control Flow Integrity (CFI) support in
the Rust compiler by providing forward-edge control flow protection for
Rust-compiled code only by aggregating function pointers in groups
identified by their return and parameter types.

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) will be provided in later work as
part of this project by identifying C char and integer type uses at the
time types are encoded (see Type metadata in the design document in the
tracking issue rust-lang#89653).

LLVM CFI can be enabled with -Zsanitizer=cfi and requires LTO (i.e.,
-Clto).

src/builder.rs

@@ -784,16 +784,6 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         // TODO(antoyo)
     }
 
-    fn type_metadata(&mut self, _function: RValue<'gcc>, _typeid: String) {
-        // Unsupported.
-    }
-
-    fn typeid_metadata(&mut self, _typeid: String) -> RValue<'gcc> {
-        // Unsupported.
-        self.context.new_rvalue_from_int(self.int_type, 0)
-    }
-
-
     fn store(&mut self, val: RValue<'gcc>, ptr: RValue<'gcc>, align: Align) -> RValue<'gcc> {
         self.store_with_flags(val, ptr, align, MemFlags::empty())
     }

src/type_.rs

@@ -1,7 +1,7 @@
 use std::convert::TryInto;
 
 use gccjit::{RValue, Struct, Type};
-use rustc_codegen_ssa::traits::{BaseTypeMethods, DerivedTypeMethods};
+use rustc_codegen_ssa::traits::{BaseTypeMethods, DerivedTypeMethods, TypeMembershipMethods};
 use rustc_codegen_ssa::common::TypeKind;
 use rustc_middle::{bug, ty};
 use rustc_middle::ty::layout::TyAndLayout;
@@ -290,3 +290,14 @@ pub fn struct_fields<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, layout: TyAndLayout
 
     (result, packed)
 }
+
+impl<'gcc, 'tcx> TypeMembershipMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
+    fn set_type_metadata(&self, _function: RValue<'gcc>, _typeid: String) {
+        // Unsupported.
+    }
+
+    fn typeid_metadata(&self, _typeid: String) -> RValue<'gcc> {
+        // Unsupported.
+        self.context.new_rvalue_from_int(self.int_type, 0)
+    }
+}