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

core/iwasm/interpreter/wasm_runtime.h

@@ -136,7 +136,6 @@ typedef struct WASMModuleInstance {
     WASIContext *wasi_ctx;
 #endif
 
-    uint32 DYNAMICTOP_PTR_offset;
     uint32 temp_ret;
     uint32 llvm_stack;