How gcc links a C program with standard libraries?

[ali hagigat]

When using standard library functions, we use some include files which
will add some extern function prototypes. But does gcc add the object
files of those functions automatically to linker?

For a regular C program in free-standing mode we have to mention the
names of the all the libraries we want to link, but how gcc can add
those standard libraries(corresponding to the functions used) without
forcing us to specify them for linker?