[CodeGen] Set attributes on resolvers emitted after ifuncs
Visiting the ifunc calls `GetOrCreateLLVMFunction` with
`NotForDefinition` while visiting the resolver calls
`GetOrCreateLLVMFunction` with `ForDefinition`.
When an ifunc is emitted before its resolver, the `ForDefinition` call
does not call `SetFunctionAttributes`, because the function prematurely
returns due to `(Entry->getValueType() == Ty)` and
`llvm::GlobalIFunc::getResolverFunctionType(DeclTy)`.
This leads to missing `!kcfi_type` with -fsanitize=kcfi.
```
extern void ifunc0(void) __attribute__ ((ifunc("resolver0")));
void *resolver0(void) { return 0; } // SetFunctionAttributes not called
extern void ifunc1(void) __attribute__ ((ifunc("resolver1")));
static void *resolver1(void) { return 0; } // SetFunctionAttributes not called
extern void ifunc2(void) __attribute__ ((ifunc("resolver2")));
static void *resolver2(void*) { return 0; }
```
Ensure `SetFunctionAttributes` is called by calling
`GetOrCreateLLVMFunction` with a dummy non-function type. Now that the
`F->takeName(Entry)` code path may be taken, the
`DisableSanitizerInstrumentation` code
(https://reviews.llvm.org/D150262) should be moved to `checkAliases`,
when the resolver function is finalized.
Pull Request: https://github.com/llvm/llvm-project/pull/98832
