[WebAssembly] Support constant offsets on loads and stores

This is just prototype for load/store for i32 types. I'll add them to
the rest of the types if we like this direction.

Differential Revision: http://reviews.llvm.org/D15197

llvm-svn: 254807
diff --git a/llvm/test/CodeGen/WebAssembly/global.ll b/llvm/test/CodeGen/WebAssembly/global.ll
index 818c454a..ffc73e3 100644
--- a/llvm/test/CodeGen/WebAssembly/global.ll
+++ b/llvm/test/CodeGen/WebAssembly/global.ll
@@ -11,7 +11,7 @@
 
 ; CHECK: foo:
 ; CHECK: i32.const $push0=, answer{{$}}
-; CHECK-NEXT: i32.load $push1=, $pop0{{$}}
+; CHECK-NEXT: i32.load $push1=, 0($pop0){{$}}
 ; CHECK-NEXT: return $pop1{{$}}
 define i32 @foo() {
   %a = load i32, i32* @answer