Fix LLVM assertion failure and update CONTRIBUTING.md (#3197)

The issue was reported in https://github.com/bytecodealliance/wasm-micro-runtime/issues/3188.

CONTRIBUTING.md

@@ -27,7 +27,7 @@ We Use Github Flow, So All Code Changes Happen Through Pull Requests. Pull reque
 Coding Style
 ===============================
 Please use [K&R](https://en.wikipedia.org/wiki/Indentation_style#K.26R) coding style, such as 4 spaces for indentation rather than tabs etc.
-We suggest use Eclipse like IDE or stable coding format tools to make your code compliant to K&R format.
+We suggest using VS Code like IDE or stable coding format tools, like clang-format, to make your code compliant to the customized format(in .clang-format).
 
 Report bugs
 ===================

core/iwasm/compilation/aot_llvm.c

@@ -1965,8 +1965,8 @@ aot_set_llvm_basic_types(AOTLLVMTypes *basic_types, LLVMContextRef context,
         basic_types->intptr_t_ptr_type = basic_types->int64_ptr_type;
     }
 
-    basic_types->gc_ref_type = LLVMPointerType(basic_types->void_type, 0);
-    basic_types->gc_ref_ptr_type = LLVMPointerType(basic_types->gc_ref_type, 0);
+    basic_types->gc_ref_type = basic_types->int8_ptr_type;
+    basic_types->gc_ref_ptr_type = basic_types->int8_pptr_type;
 
     return (basic_types->int8_ptr_type && basic_types->int8_pptr_type
             && basic_types->int16_ptr_type && basic_types->int32_ptr_type