[WebAssembly] Add target feature for atomics

Summary:
This tracks the WebAssembly threads feature proposal at
https://github.com/WebAssembly/threads/blob/master/proposals/threads/Overview.md

Differential Revision: https://reviews.llvm.org/D37300

llvm-svn: 312145
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblySetP2AlignOperands.cpp b/llvm/lib/Target/WebAssembly/WebAssemblySetP2AlignOperands.cpp
index b1385f4..a418f65 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblySetP2AlignOperands.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblySetP2AlignOperands.cpp
@@ -96,6 +96,7 @@
       case WebAssembly::LOAD16_U_I64:
       case WebAssembly::LOAD32_S_I64:
       case WebAssembly::LOAD32_U_I64:
+      case WebAssembly::ATOMIC_LOAD_I32:
         RewriteP2Align(MI, WebAssembly::LoadP2AlignOperandNo);
         break;
       case WebAssembly::STORE_I32: