[WebAssembly] Add exception and selector intrinsics

[aheejin]

Summary

Since wasm EH does not use landingpad instructions, these instructions
provide exception pointer and selector values until we lower them in
WasmEHPrepare.

llvm/trunk/include/llvm/IR/IntrinsicsWebAssembly.td

 //===----------------------------------------------------------------------===//
 // Exception handling intrinsics
 //===----------------------------------------------------------------------===//
 
 // throw / rethrow
 def int_wasm_throw : Intrinsic<[], [llvm_i32_ty, llvm_ptr_ty],
                                [Throws, IntrNoReturn]>;
 def int_wasm_rethrow : Intrinsic<[], [], [Throws, IntrNoReturn]>;
+
+// Since wasm does not use landingpad instructions, these instructions return
+// exception pointer and selector values until we lower them in WasmEHPrepare.
+def int_wasm_get_exception : Intrinsic<[llvm_ptr_ty], [], [IntrHasSideEffects]>;
+def int_wasm_get_ehselector : Intrinsic<[llvm_i32_ty], [],
+                                        [IntrHasSideEffects]>;
 }