Makefile.in: Remove all references to s-under and underscore.c.

Makefile.in: Remove all references to s-under and underscore.c.

gcc:
	* Makefile.in: Remove all references to s-under and underscore.c.
	* collect2.c, tlink.c: Change all uses of prepends_underscore
	to look directly at USER_LABEL_PREFIX.

gcc/cp:
	* Make-lang.in: Build cp/cxxfilt.o from $(srcdir)/cp/cxxfilt.c,
	and c++filt from cxxfilt.o + version.o + $(LIBDEPS).
	* cxxfilt.c: New file: split from libiberty/cplus-dem.c, with
	minor adjustments (use version_string, eliminate yet another
	duplicate of xmalloc)

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.

From-SVN: r57037