Use obstack_strdup more

Use obstack_strdup more

This changes gdb to use obstack_strdup when appropriate, rather than
the wordier obstack_copy0.

gdb/ChangeLog
2019-08-06  Tom Tromey  <tom@tromey.com>

	* xcoffread.c (SYMNAME_ALLOC, process_xcoff_symbol): Use
	obstack_strdup.
	* typeprint.c (typedef_hash_table::find_global_typedef): Use
	obstack_strdup.
	* symfile.c (allocate_compunit_symtab): Use obstack_strdup.
	* stabsread.c (common_block_start): Use obstack_strdup.
	* objfiles.c (set_objfile_main_name, objfile): Use
	obstack_strdup.
	* namespace.c (add_using_directive): Use obstack_strdup.
	* mdebugread.c (parse_symbol, parse_type): Use obstack_strdup.
	* jit.c (finalize_symtab): Use obstack_strdup.
	* dwarf2read.c (fixup_go_packaging, dwarf2_physname)
	(guess_partial_die_structure_name, partial_die_info::fixup)
	(dwarf2_name): Use obstack_strdup.
	* coffread.c (coff_read_struct_type, coff_read_enum_type): Use
	obstack_strdup.
	* c-exp.y (scan_macro_expansion): Use obstack_strdup.
	* buildsym.c (buildsym_compunit::end_symtab_with_blockvector): Use
	obstack_strdup.
	* ada-lang.c (ada_decode_symbol): Use obstack_strdup.