[Bug] Fix breakages that occur when targeting WASM with Emscripten. (#422)

We don't import either architecture in archtraits so include
environment.h to ensure Environment is visible, and don't use
__builtin__clear_cache in Emscripten because it's unsupported.

src/asmjit/core/archtraits.cpp

@@ -5,6 +5,7 @@
 
 #include "../core/api-build_p.h"
 #include "../core/archtraits.h"
+#include "../core/environment.h"
 #include "../core/misc_p.h"
 
 #if !defined(ASMJIT_NO_X86)

src/asmjit/core/virtmem.cpp

@@ -852,7 +852,7 @@ Error releaseDualMapping(DualMapping* dm, size_t size) noexcept {
 // ========================================
 
 void flushInstructionCache(void* p, size_t size) noexcept {
-#if ASMJIT_ARCH_X86
+#if ASMJIT_ARCH_X86 || defined(__EMSCRIPTEN__)
   // X86/X86_64 architecture doesn't require to do anything to flush instruction cache.
   DebugUtils::unused(p, size);
 #elif defined(__APPLE__)