Perform all tests in callfuncs.exp with and without C function prototypes

Perform all tests in callfuncs.exp with and without C function prototypes

In callfuncs.exp, compile callfuncs.c with and without C function
header prototypes and execute all tests after each compilation.

gdb/testsuite/ChangeLog:

	* gdb.base/callfuncs.exp: Remove 'prototypes' variable.  Move main
	logic into perform_all_tests() and invoke it with and without
	function header prototypes.
	(do_function_calls): Remove conditional XFAIL for PR 5318.
	(rerun_and_prepare): Remove duplicate code.
	(perform_all_tests): New.  Main logic moved here.