Unity 5 WebGL build error with _llvm_memcpy_p0i8_p0i8_i32 is not defined

For what its worth, I ran into this same issue.

While i cannot speak 100% for full exceptions being completely broken, I can confirm at least for me that the exceptions that i've ran into with full exceptions enabled always result in this error code.

So if you're running into this exact error you'd likely be better off with full exceptions off. Where when I get this error without full exceptions i at least get a somewhat more informative error.

In my case with full exceptions on:

 "exception thrown: ReferenceError: _llvm_memcpy_p0i8_p0i8_i32 is not defined,_llvm_memcpy_p0i8_p0i8_i32__wrapper@http://localhost:63510/Development/Html5.js:5722554:2
 dynCall_viiiii@http://localhost:63510/Development/Html5.js:5722039:2
 invoke_viiiii@http://localhost:63510/Development/Html5.js:15412:3
 __Z16File__ctor_m3223P9File_t378bP11Reader_t783P10MethodInfo@http://localhost:63510/Development/Html5.js:2595212:14
 dynCall_viiii@http://localhost:63510/Development/Html5.js:5728069:2
 invoke_viiii@http://localhost:63510/Development/Html5.js:15404:3
 __Z16File__ctor_m1008P9File_t378P11Stream_t775P10MethodInfo@http://localhost:63510/Development/Html5.js:4953675:6
 dynCall_viii@http://localhost:63510/Development/Html5.js:5737131:2
 invoke_viii@http://localhost:63510/Development/Html5.js:15788:3
 __Z27PlayerRoutine_MoveNext_m523P18PlayerRoutine_t218P10MethodInfo@http://localhost:63510/Development/Html5.js:2198517:6
 __ZN16VirtFuncInvoker0IbE6InvokeEP10MethodInfoPv@http://localhost:63510/Development/Html5.js:5617012:7
 dynCall_iii@http://localhost:63510/Development/Html5.js:5740955:9
 invoke_iii@http://localhost:63510/Development/Html5.js:15700:10
 __Z22SongPlayer_Update_m529P15SongPlayer_t181P10MethodInfo@http://localhost:63510/Development/Html5.js:5479254:3
 __Z24RuntimeInvoker_Void_t222P10MethodInfoPvPS1_@http://localhost:63510/Development/Html5.js:5721364:2
 dynCall_iiii@http://localhost:63510/Development/Html5.js:5734288:9
 invoke_iiii@http://localhost:63510/Development/Html5.js:16052:10
 __ZN6il2cpp2vm7Runtime6InvokeEP10MethodInfoPvPS4_PP12Il2CppObject@http://localhost:63510/Development/Html5.js:5455514:7
 _il2cpp_runtime_invoke@http://localhost:63510/Development/Html5.js:5710236:7
 __Z23scripting_method_invoke21ScriptingMethodIl2CppP15ScriptingObjectR18ScriptingArgumentsPP18ScriptingException@http://localhost:63510/Development/Html5.js:5648018:7
 __ZN25ScriptingInvocationNoArgs6InvokeEPP18ScriptingException@http://localhost:63510/Development/Html5.js:4617123:7
 __ZN25ScriptingInvocationNoArgs6InvokeEv@http://localhost:63510/Development/Html5.js:5685605:7
 __ZN13MonoBehaviour16CallUpdateMethodEi@http://localhost:63510/Development/Html5.js:4483405:2
 __ZN13MonoBehaviour6UpdateEv@http://localhost:63510/Development/Html5.js:5735407:2
 __ZN20BaseBehaviourManager12CommonUpdateI16BehaviourManagerEEvv@http://localhost:63510/Development/Html5.js:4029994:4
 __ZN16BehaviourManager6UpdateEv@http://localhost:63510/Development/Html5.js:5727144:2
 dynCall_vi@http://localhost:63510/Development/Html5.js:5748531:2
 invoke_vi@http://localhost:63510/Development/Html5.js:15868:3
 __Z10PlayerLoopbbP10IHookEvent@http://localhost:63510/Development/Html5.js:2073917:8
 __ZL8mainloopv@http://localhost:63510/Development/Html5.js:5534247:2
 dynCall_v@http://localhost:63510/Development/Html5.js:5751775:2
 Runtime.dynCall@http://localhost:63510/Development/Html5.js:206:11
 Browser_mainLoop_runner/<@http://localhost:63510/Development/Html5.js:10294:5
 Browser.mainLoop.runIter@http://localhost:63510/Development/Html5.js:7063:5
 Browser_mainLoop_runner@http://localhost:63510/Development/Html5.js:10290:3
 "

With full exceptions off:

 "exception thrown: TypeError: sound.buffer is null,_JS_Sound_GetLength@http://localhost:63251/Development/Html5.js:11094:2
 __ZN4FMOD7SystemI9playSoundE17FMOD_CHANNELINDEXPNS_5SoundEbPPNS_7ChannelE@http://localhost:63251/Development/Html5.js:1414225:23
 __ZN4FMOD6System9playSoundE17FMOD_CHANNELINDEXPNS_5SoundEbPPNS_7ChannelE@http://localhost:63251/Development/Html5.js:2061184:9
 __ZN11SoundHandle8Instance13CreateChannelERS_b@http://localhost:63251/Development/Html5.js:559983:8
 __ZN11SoundHandle13CreateChannelEb@http://localhost:63251/Development/Html5.js:2191737:4
 __ZN10SampleClip15AllocateChannelEby@http://localhost:63251/Development/Html5.js:2099778:2
 __ZN11AudioSource4PlayEd@http://localhost:63251/Development/Html5.js:593600:4
 __Z32AudioSource_CUSTOM_PlayScheduledP15ScriptingObjectd@http://localhost:63251/Development/Html5.js:2344020:4
 __Z31AudioSource_PlayScheduled_m1015P15AudioSource_t56dP10MethodInfo@http://localhost:63251/Development/Html5.js:2391493:2
 __Z27PlayerRoutine_MoveNext_m523P18PlayerRoutine_t218P10MethodInfo@http://localhost:63251/Development/Html5.js:675471:6
 __ZN16VirtFuncInvoker0IbE6InvokeEP10MethodInfoPv@http://localhost:63251/Development/Html5.js:2338764:7
 __Z22SongPlayer_Update_m529P15SongPlayer_t181P10MethodInfo@http://localhost:63251/Development/Html5.js:2453924:2
 __Z24RuntimeInvoker_Void_t222P10MethodInfoPvPS1_@http://localhost:63251/Development/Html5.js:2464920:2
 __ZN6il2cpp2vm7Runtime6InvokeEP10MethodInfoPvPS4_PP12Il2CppObject@http://localhost:63251/Development/Html5.js:2412562:7
 _il2cpp_runtime_invoke@http://localhost:63251/Development/Html5.js:2444676:7
 __Z23scripting_method_invoke21ScriptingMethodIl2CppP15ScriptingObjectR18ScriptingArgumentsPP18ScriptingException@http://localhost:63251/Development/Html5.js:2375623:7
 __ZN25ScriptingInvocationNoArgs6InvokeEPP18ScriptingException@http://localhost:63251/Development/Html5.js:1656774:7
 __ZN25ScriptingInvocationNoArgs6InvokeEv@http://localhost:63251/Development/Html5.js:2410126:7
 __ZN13MonoBehaviour16CallUpdateMethodEi@http://localhost:63251/Development/Html5.js:1511585:2
 __ZN13MonoBehaviour6UpdateEv@http://localhost:63251/Development/Html5.js:2489077:2
 __ZN20BaseBehaviourManager12CommonUpdateI16BehaviourManagerEEvv@http://localhost:63251/Development/Html5.js:1224661:4
 __ZN16BehaviourManager6UpdateEv@http://localhost:63251/Development/Html5.js:2474005:2
 __Z10PlayerLoopbbP10IHookEvent@http://localhost:63251/Development/Html5.js:536275:3
 __ZL8mainloopv@http://localhost:63251/Development/Html5.js:2235921:2
 dynCall_v@http://localhost:63251/Development/Html5.js:2513589:2
 Runtime.dynCall@http://localhost:63251/Development/Html5.js:206:11
 Browser_mainLoop_runner/<@http://localhost:63251/Development/Html5.js:10281:5
 Browser.mainLoop.runIter@http://localhost:63251/Development/Html5.js:7048:5
 Browser_mainLoop_runner@http://localhost:63251/Development/Html5.js:10277:3
 "

Each of these stack traces occur in different areas, but I've confirmed that the first trace (with full on) does not throw any exception at all with full exceptions enabled. and have confirmed with other community members that the second error is expected ( http://forum.unity3d.com/threads/audioclip-create.317032/ )

tl;dr version: afaik full exceptions is broke (as of 5.0.1f1) and its likely only misdirecting you. use developer builds with enable exceptions as None to better determine the issue.

This is a bug in emscripten, it will be fixed in Unity 5.1.