libc-builtin: Fix the signature of strncasecmp native function (#888)

Fix the signature invalid issue in libc-builtin, modify signature of strncasecmp
native function from "($$i)" to "($$i)i".

core/iwasm/libraries/libc-builtin/libc_builtin_wrapper.c

@@ -1161,7 +1161,7 @@ static NativeSymbol native_symbols_libc_builtin[] = {
     REG_NATIVE_FUNC(strtol, "($*i)i"),
     REG_NATIVE_FUNC(strtoul, "($*i)i"),
     REG_NATIVE_FUNC(memchr, "(*ii)i"),
-    REG_NATIVE_FUNC(strncasecmp, "($$i)"),
+    REG_NATIVE_FUNC(strncasecmp, "($$i)i"),
     REG_NATIVE_FUNC(strspn, "($$)i"),
     REG_NATIVE_FUNC(strcspn, "($$)i"),
     REG_NATIVE_FUNC(strstr, "($$)i"),