PR29925, Memory leak in find_abstract_instance

PR29925, Memory leak in find_abstract_instance

The testcase in the PR had a variable with both DW_AT_decl_file and
DW_AT_specification, where the DW_AT_specification also specified
DW_AT_decl_file.  This leads to a memory leak as the file name is
malloced and duplicates are not expected.

I've also changed find_abstract_instance to not use a temp for "name",
because that can result in a change in behaviour from the usual last
of duplicate attributes wins.

	PR 29925
	* dwarf2.c (find_abstract_instance): Delete "name" variable.
	Free *filename_ptr before assigning new file name.
	(scan_unit_for_symbols): Similarly free func->file and
	var->file before assigning.