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/compilation/aot_llvm.h

@@ -102,6 +102,8 @@ typedef struct AOTFuncContext {
   LLVMValueRef aot_inst;
   LLVMValueRef table_base;
   LLVMValueRef argv_buf;
+  LLVMValueRef native_stack_bound;
+  LLVMValueRef last_alloca;
 
   LLVMValueRef heap_base_offset;
   LLVMValueRef mem_base_addr;