[Clang] Add an empty builtins.h file.

[stefanp]

Summary

On Power PC some legacy compilers included a number of builtins in a
builtins.h header file. While this header file is not required to hold
builtins for clang some legacy code does try to include this file and so
this patch provides an empty version of that file.

[nemanjai]

clang/lib/Headers/builtins.h

9

Please describe the purpose of this header file in a comment here.

clang/test/Headers/builtins-header.c

2

Does this need something like REQUIRES: powerpc-registered-target?

[stefanp]

Added comment to the builtins.h file.

[stefanp]

clang/test/Headers/builtins-header.c

2

I don't think so... but I could be wrong. I am testing this using the Power PC triple but in reality there is nothing specifically Power PC about this header file. I think that it can be included on any target.

[nemanjai]

LGTM.

clang/lib/Headers/CMakeLists.txt

set(files
   avx512vlvp2intersectintrin.h
   avx512vpopcntdqvlintrin.h
   avx512vnniintrin.h
   avx512vlvnniintrin.h
   avxintrin.h
   avxvnniintrin.h
   bmi2intrin.h
   bmiintrin.h
+  builtins.h
   __clang_cuda_builtin_vars.h
   __clang_cuda_math.h
   __clang_cuda_cmath.h
   __clang_cuda_complex_builtins.h
   __clang_cuda_device_functions.h
   __clang_cuda_intrinsics.h
   __clang_cuda_libdevice_declares.h
   __clang_cuda_math_forward_declares.h

clang/lib/Headers/builtins.h

+/*===---- builtins.h - Standard header for extra builtins -----------------===*\
+ *
+ * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+ * See https://llvm.org/LICENSE.txt for license information.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+\*===----------------------------------------------------------------------===*/
+
+/// Some legacy compilers have builtin definitions in a file named builtins.h.
+/// This header file has been added to allow compatibility with code that was
+/// written for those compilers. Code may have an include line for this file
+/// and to avoid an error an empty file with this name is provided.
+#ifndef __BUILTINS_H
+#define __BUILTINS_H
+
+#endif /* __BUILTINS_H */

clang/test/Headers/builtins-header.c

+// RUN: %clang_cc1 -triple powerpc64-unknown-unknown -ffreestanding -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple powerpc64le-unknown-unknown -ffreestanding -emit-llvm -o - %s | FileCheck %s
+
+#include <builtins.h>
+
+// Verify that we can include <builtins.h>
+
+// CHECK: target triple = "powerpc64