WebAssembly: add placeholder intrinsics header

[sunfish]

include/llvm/IR/IntrinsicsWebAssembly.td

10

Triple-slash comments, \file, and \brief? I know no other targets do that, but we could start a new trend :-).

14

Other targets have a comment like this:

// All intrinsics start with "llvm.wasm.".

which is nice.

[jfb]

• Address sunfish's comments.

include/llvm/IR/Intrinsics.td

 include "llvm/IR/IntrinsicsAArch64.td"
 include "llvm/IR/IntrinsicsXCore.td"
 include "llvm/IR/IntrinsicsHexagon.td"
 include "llvm/IR/IntrinsicsNVVM.td"
 include "llvm/IR/IntrinsicsMips.td"
 include "llvm/IR/IntrinsicsAMDGPU.td"
 include "llvm/IR/IntrinsicsBPF.td"
 include "llvm/IR/IntrinsicsSystemZ.td"
+include "llvm/IR/IntrinsicsWebAssembly.td"

include/llvm/IR/IntrinsicsWebAssembly.td

+//===- IntrinsicsWebAssembly.td - Defines wasm intrinsics --*- tablegen -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines all of the WebAssembly-specific intrinsics.
+//
+//===----------------------------------------------------------------------===//
+
+let TargetPrefix = "wasm" in {
+}