Stop emitting CET prologues for naked functions

We can apply nocf_check as a hack for now.

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -299,6 +299,10 @@ pub fn from_fn_attrs<'ll, 'tcx>(
     }
     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
         to_add.push(AttributeKind::Naked.create_attr(cx.llcx));
+        // HACK(jubilee): "indirect branch tracking" works by attaching prologues to functions.
+        // And it is a module-level attribute, so the alternative is pulling naked functions into new LLVM modules.
+        // Otherwise LLVM's "naked" functions come with endbr prefixes per https://github.com/rust-lang/rust/issues/98768
+        to_add.push(AttributeKind::NoCfCheck.create_attr(cx.llcx));
     }
     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
         // apply to return place instead of function (unlike all other attributes applied in this function)

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -191,6 +191,7 @@ pub enum AttributeKind {
     StackProtect = 32,
     NoUndef = 33,
     SanitizeMemTag = 34,
+    NoCfCheck = 35,
 }
 
 /// LLVMIntPredicate

compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h

@@ -84,6 +84,7 @@ enum LLVMRustAttribute {
   StackProtect = 32,
   NoUndef = 33,
   SanitizeMemTag = 34,
+  NoCfCheck = 35,
 };
 
 typedef struct OpaqueRustString *RustStringRef;

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -176,6 +176,8 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
     return Attribute::NoAlias;
   case NoCapture:
     return Attribute::NoCapture;
+  case NoCfCheck:
+    return Attribute::NoCfCheck;
   case NoInline:
     return Attribute::NoInline;
   case NonNull: