Get rid of underscore.c

[Richard Earnshaw]

libiberty:
	* cplus-dem.c: Code code under #ifdef MAIN moved to gcc/cp/cxxfilt.c.
	* testsuite/Makefile.in: Adjust for test-demangle.
	* testsuite/regress-demangle: Deleted.
	* testsuite/test-demangle.c: New file.
	* testsuite/demangle-expected: Change \$ to $ throughout, now that
	this file is not being read by a shell script.


This has just broken binutils builds.  Binutils currently builds its own 
copy of cxxfilt and now it has no main function.