Disassemble blocks with non-contiguous ranges

Disassemble blocks with non-contiguous ranges

This patch adds support for disassembly of blocks with non-contiguous
ranges.  These blocks are printed as follows:

(gdb) disassemble foo
Dump of assembler code for function foo:
Address range 0x401136 to 0x401151:
   0x0000000000401136 <+0>:     push   %rbp
   0x0000000000401137 <+1>:     mov    %rsp,%rbp
   0x000000000040113a <+4>:     callq  0x401134 <bar>
   0x000000000040113f <+9>:     mov    0x2eef(%rip),%eax        # 0x404034 <e>
   0x0000000000401145 <+15>:    test   %eax,%eax
   0x0000000000401147 <+17>:    je     0x40114e <foo+24>
   0x0000000000401149 <+19>:    callq  0x401128 <foo+4294967282>
   0x000000000040114e <+24>:    nop
   0x000000000040114f <+25>:    pop    %rbp
   0x0000000000401150 <+26>:    retq
Address range 0x401128 to 0x401134:
   0x0000000000401128 <+-14>:   push   %rbp
   0x0000000000401129 <+-13>:   mov    %rsp,%rbp
   0x000000000040112c <+-10>:   callq  0x401126 <baz>
   0x0000000000401131 <+-5>:    nop
   0x0000000000401132 <+-4>:    pop    %rbp
   0x0000000000401133 <+-3>:    retq
End of assembler dump.

This is an actual dump from the test case that I constructed for
this work.  The ranges are printed in the order encountered in the
debug info. For the above example, note that the second range occupies
lower addresses than the first range.

Functions with contiguous ranges are still printed as follows:

(gdb) disassemble main
Dump of assembler code for function main:
   0x0000000000401151 <+0>:     push   %rbp
   0x0000000000401152 <+1>:     mov    %rsp,%rbp
   0x0000000000401155 <+4>:     callq  0x401136 <foo>
   0x000000000040115a <+9>:     mov    $0x0,%eax
   0x000000000040115f <+14>:    pop    %rbp
   0x0000000000401160 <+15>:    retq
End of assembler dump.

gdb/ChangeLog:

	* cli/cli-cmds.c (block.h): Include.
	(print_disassembly): Handle printing of non-contiguous blocks.
	(disassemble_current_function): Likewise.
	(disassemble_command): Likewise.