* gdb.c++/*.exp: Warn if executable does not exist. The original

	* gdb.c++/*.exp: Warn if executable does not exist.  The original
	reason for skipping the warning was that configure.in sometimes
	intentionally skipped building the executables but the tcl code
	had no way of knowing.  That (a) was always bogus with respect to
	error handling, (b) is no longer true (right now there is no way
	to skip C++ tests).

	* gdb.c++/demangle.exp: Remove unused binfile and srcfile variables.