[Clang][CodeGen] Introduce the AllocToken SanitizerKind (llvm#162098)

[ Reland after 7815df1 ("[Clang] Fix brittle print-header-json.c test") ]

Introduce the "alloc-token" sanitizer kind, in preparation of wiring it
up. Currently this is a no-op, and any attempt to enable it will result
in failure:

clang: error: unsupported option '-fsanitize=alloc-token' for target
'x86_64-unknown-linux-gnu'

In this step we can already wire up the `sanitize_alloc_token` IR
attribute where the instrumentation is enabled. Subsequent changes will
complete wiring up the AllocToken pass.

---

This change is part of the following series:
  1. llvm#160131
  2. llvm#156838
  3. llvm#162098
  4. llvm#162099
  5. llvm#156839
  6. llvm#156840
  7. llvm#156841
  8. llvm#156842

Author: melver

clang/include/clang/Basic/Sanitizers.def

@@ -195,6 +195,9 @@ SANITIZER_GROUP("bounds", Bounds, ArrayBounds | LocalBounds)
 // Scudo hardened allocator
 SANITIZER("scudo", Scudo)
 
+// AllocToken
+SANITIZER("alloc-token", AllocToken)
+
 // Magic group, containing all sanitizers. For example, "-fno-sanitize=all"
 // can be used to disable all the sanitizers.
 SANITIZER_GROUP("all", All, ~SanitizerMask())

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -846,6 +846,8 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
       Fn->addFnAttr(llvm::Attribute::SanitizeNumericalStability);
     if (SanOpts.hasOneOf(SanitizerKind::Memory | SanitizerKind::KernelMemory))
       Fn->addFnAttr(llvm::Attribute::SanitizeMemory);
+    if (SanOpts.has(SanitizerKind::AllocToken))
+      Fn->addFnAttr(llvm::Attribute::SanitizeAllocToken);
   }
   if (SanOpts.has(SanitizerKind::SafeStack))
     Fn->addFnAttr(llvm::Attribute::SafeStack);