[clang] [Clang] __has_builtin should return false for aux triple builtins (PR #121839)

[Nick Sarnie via cfe-commits]

sarnex wrote:

> Is it possible that we could just skip generating the builtin IDs at all for the aux target? Or does that break something.

Seems like we can't, I tried this:
```
diff --git a/clang/lib/Basic/Builtins.cpp b/clang/lib/Basic/Builtins.cpp
index c6e54b89e848..904c64f05c36 100644
--- a/clang/lib/Basic/Builtins.cpp
+++ b/clang/lib/Basic/Builtins.cpp
@@ -64,8 +64,8 @@ void Builtin::Context::InitializeTarget(const TargetInfo &Target,
                                         const TargetInfo *AuxTarget) {
   assert(TSRecords.empty() && "Already initialized target?");
   TSRecords = Target.getTargetBuiltins();
-  if (AuxTarget)
-    AuxTSRecords = AuxTarget->getTargetBuiltins();
+  //  if (AuxTarget)
+  //  AuxTSRecords = AuxTarget->getTargetBuiltins();
 }
```
and got these failures
```
Failed Tests (3):
  Clang :: CodeGenHipStdPar/unsupported-builtins.cpp
  Clang :: Headers/__cpuidex_conflict.c
  Clang :: Sema/builtin-spirv-amdgcn-atomic-inc-dec-failure.cpp
```

and then reverted that and tried this
```
diff --git a/clang/lib/Basic/Builtins.cpp b/clang/lib/Basic/Builtins.cpp
index c6e54b89e848..34e1d0aa4b68 100644
--- a/clang/lib/Basic/Builtins.cpp
+++ b/clang/lib/Basic/Builtins.cpp
@@ -153,9 +153,9 @@ void Builtin::Context::initializeBuiltins(IdentifierTable &Table,
       Table.get(TSRecords[i].Name).setBuiltinID(i + Builtin::FirstTSBuiltin);
 
   // Step #3: Register target-specific builtins for AuxTarget.
-  for (unsigned i = 0, e = AuxTSRecords.size(); i != e; ++i)
-    Table.get(AuxTSRecords[i].Name)
-        .setBuiltinID(i + Builtin::FirstTSBuiltin + TSRecords.size());
+  //for (unsigned i = 0, e = AuxTSRecords.size(); i != e; ++i)
+  //  Table.get(AuxTSRecords[i].Name)
+  //      .setBuiltinID(i + Builtin::FirstTSBuiltin + TSRecords.size());
 
   // Step #4: Unregister any builtins specified by -fno-builtin-foo.
   for (llvm::StringRef Name : LangOpts.NoBuiltinFuncs) {

```
and got it broke the same tests
```
Failed Tests (3):
  Clang :: CodeGenHipStdPar/unsupported-builtins.cpp
  Clang :: Headers/__cpuidex_conflict.c
  Clang :: Sema/builtin-spirv-amdgcn-atomic-inc-dec-failure.cpp

```

https://github.com/llvm/llvm-project/pull/121839