Apply noundef attribute to &T, &mut T, Box<T>, bool

This doesn't handle `char` because it's a bit awkward to distinguish it
from u32 at this point in codegen.

Note that for some types (like `&Struct` and `&mut Struct`),
we already apply `dereferenceable`, which implies `noundef`,
so the IR does not change.

compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h

@@ -82,6 +82,7 @@ enum LLVMRustAttribute {
   StackProtectReq = 30,
   StackProtectStrong = 31,
   StackProtect = 32,
+  NoUndef = 33,
 };
 
 typedef struct OpaqueRustString *RustStringRef;

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -224,6 +224,8 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
     return Attribute::StackProtectStrong;
   case StackProtect:
     return Attribute::StackProtect;
+  case NoUndef:
+    return Attribute::NoUndef;
   }
   report_fatal_error("bad AttributeKind");
 }