First of all, thank you for listening to this mail.
As I mentioned in the title, I got a undefined reference in compiling time.
The reason that I wonder is that I surely add header file for the function.
In more detail,
I want to use TransactionIdEquals() function in freelist.c file.
Then, I included a header file, "access/xact.h" for the function.
However, in make command, compiler send implicit declaration of function
warning and then undefined reference at linking time.
How could I overcome this problem? :(