Implement post-MVP features and native stack overflow check (#243)

Implement native thread stack overflow check
Implement post-MVP: Non-trapping float-to-int conversions
Implement post-MVP: Sign-extension operators
Enhance WASM loader checks

build-scripts/config_common.cmake

@@ -124,3 +124,7 @@ else ()
   message ("     Fast interpreter disabled")
 endif ()
 
+if (WAMR_BUILD_SPEC_TEST EQUAL 1)
+  add_definitions (-DWASM_ENABLE_SPEC_TEST=1)
+  message ("     spec test compatible mode is on")
+endif()