add splay tree for info_ptr -> CU mapping

add splay tree for info_ptr -> CU mapping

While using perf top for MozillaThunderbird I noticed quite some slow
dissably call with source code involved. E.g.

time ./objdump --start-address=0x0000000004e0dcd0 --stop-address=0x0000000004e0df8b -l -d --no-show-raw-insn -S -C /usr/lib64/thunderbird/libxul.so

took 2.071s and I noticed quite some time is spent in
find_abstract_instance:

    33.46%  objdump  objdump               [.] find_abstract_instance
    18.22%  objdump  objdump               [.] arange_add
    13.77%  objdump  objdump               [.] read_attribute_value
     4.82%  objdump  objdump               [.] comp_unit_maybe_decode_line_info
     3.10%  objdump  libc.so.6             [.] __memset_avx2_unaligned_erms

where linked list of CU is iterated when searing for where info_ptr
belongs to:

         : 3452   for (u = unit->prev_unit; u != NULL; u = u->prev_unit)
    0.00 :   4c61f7: mov    0x10(%rbx),%rax
    0.00 :   4c61fb: test   %rax,%rax
    0.00 :   4c61fe: je     4c6215 <find_abstract_instance+0x365>
         : 3453   if (info_ptr >= u->info_ptr_unit && info_ptr < u->end_ptr)
    0.00 :   4c6200: cmp    0x60(%rax),%rdx
   83.20 :   4c6204: jb     4c620c <find_abstract_instance+0x35c>
    0.00 :   4c6206: cmp    0x78(%rax),%rdx
    6.89 :   4c620a: jb     4c6270 <find_abstract_instance+0x3c0>
         : 3452   for (u = unit->prev_unit; u != NULL; u = u->prev_unit)
    0.00 :   4c620c: mov    0x10(%rax),%rax
    7.90 :   4c6210: test   %rax,%rax
    0.00 :   4c6213: jne    4c6200 <find_abstract_instance+0x350>

The following scan can be replaced with search in a splay tree and with
that I can get to 1.5s and there are other symbols where the difference
is even bigger.

bfd/ChangeLog:

	PR 29081
	* dwarf2.c (struct addr_range): New.
	(addr_range_intersects): Likewise.
	(splay_tree_compare_addr_range): Likewise.
	(splay_tree_free_addr_range): Likewise.
	(struct dwarf2_debug_file): Add comp_unit_tree.
	(find_abstract_instance): Use the splay tree when searching
	for a info_ptr.
	(stash_comp_unit): Insert to the splay tree.
	(_bfd_dwarf2_cleanup_debug_info): Clean up the splay tree.