Eliminate literal line numbers in call-rt-st.exp

Eliminate literal line numbers in call-rt-st.exp

Remove literal line numbers from the regexps in call-rt-st.exp.  Add
appropriate eye-catchers to call-rt-st.c and refer to those instead.

gdb/testsuite/ChangeLog:

	* gdb.base/call-rt-st.c: Add eye-catchers.
	* gdb.base/call-rt-st.exp: Refer to eye-catchers instead of
	literal line numbers.