re PR c++/13241 ([ABI] Incorrect mangling of template arguments)

re PR c++/13241 ([ABI] Incorrect mangling of template arguments)

cp:
	PR c++/13241
	C++ ABI change. Mangling of symbols in expressions.
	* mangle.c (write_mangled_name): Add top_level flag. Rework for
	nested and unnested mangling. Deal with abi version 1 and version
	2 differences.
	(write_expression): Adjust write_mangled_name call.
	(mangle_decl_string): Use write_mangled_name for all non-type decls.
testsuite:
	PR c++/13241
	* g++.dg/abi/mangle18-1.C: New test.
	* g++.dg/abi/mangle18-2.C: New test.

From-SVN: r74628