Further workarounds for binutils/15021.

	Further workarounds for binutils/15021.
	* dwarf2read.c (recursively_compute_inclusions): Change type of result
	parameter to VEC (symtab_ptr) **.  New parameter all_type_symtabs.
	Watch for duplicate symtabs coming from type units.
	(compute_symtab_includes): Update call to
	recursively_compute_inclusions. Build vector of included symtabs
	instead of per_cus.
	* symtab.h (symtab_ptr): New typedef.
	(DEF_VEC_P (symtab_ptr)): New VEC type.
	* linespec.c (symtab_p): Delete.  All uses updated to use symtab_ptr
	instead.