bug#24703: Store references in 8-byte chunks in compiled code

[Mark H Weaver <mhw@netris.org>]

Here's what happens with a variant of 'unixodbc' with one character
removed from its name, to make an odd number of characters.  The last
character 'c' is all by itself.  The chunks of the reference

  /gnu/store/il1bn7n0l4yj3idrii23fhvzg4nn939i-unxodbc-2.3.4/etc

are found in the following order:

1_/gnu/sto
2_________________________________________________________4/et
3_________re/il1bn
4_________________7n0l4yj3
5_________________________idrii23f
6_________________________________hvzg4nn9
7_________________________________________39i-unxo
8_________________________________________________dbc-2.3.
9_____________________________________________________________c

======== /gnu/store/y2dwj5vkbxka7y5rlakprbk4k8vrd5ij-unxodbc-2.3.4/lib/libodbcinst.so.2.0.0
    8238:	48 b8 2f 67 6e 75 2f 	movabs $0x6f74732f756e672f,%rax   ; "/gnu/sto"
    823f:	73 74 6f 
    8242:	c7 05 6c fa 20 00 34 	movl   $0x74652f34,0x20fa6c(%rip) ; "4/et"
    8249:	2f 65 74 
    824c:	c7 05 2e 0a 21 00 01 	movl   $0x1,0x210a2e(%rip)
    8253:	00 00 00 
    8256:	48 89 05 23 fa 20 00 	mov    %rax,0x20fa23(%rip)
    825d:	48 b8 72 65 2f 69 6c 	movabs $0x6e62316c692f6572,%rax   ; "re/il1bn"
    8264:	31 62 6e 
    8267:	48 8d 1d 5a 94 00 00 	lea    0x945a(%rip),%rbx
    826e:	48 89 05 13 fa 20 00 	mov    %rax,0x20fa13(%rip)
    8275:	48 b8 37 6e 30 6c 34 	movabs $0x336a79346c306e37,%rax   ; "7n0l4yj3"
    827c:	79 6a 33 
    827f:	48 89 05 0a fa 20 00 	mov    %rax,0x20fa0a(%rip)
    8286:	48 b8 69 64 72 69 69 	movabs $0x6633326969726469,%rax   ; "idrii23f"
    828d:	32 33 66 
    8290:	48 89 05 01 fa 20 00 	mov    %rax,0x20fa01(%rip)
    8297:	48 b8 68 76 7a 67 34 	movabs $0x396e6e34677a7668,%rax   ; "hvzg4nn9"
    829e:	6e 6e 39 
    82a1:	48 89 05 f8 f9 20 00 	mov    %rax,0x20f9f8(%rip)
    82a8:	48 b8 33 39 69 2d 75 	movabs $0x6f786e752d693933,%rax   ; "39i-unxo"
    82af:	6e 78 6f 
    82b2:	48 89 05 ef f9 20 00 	mov    %rax,0x20f9ef(%rip)
    82b9:	48 b8 64 62 63 2d 32 	movabs $0x2e332e322d636264,%rax   ; "dbc-2.3."
    82c0:	2e 33 2e 
    82c3:	48 89 05 e6 f9 20 00 	mov    %rax,0x20f9e6(%rip)
    82ca:	b8 63 00 00 00       	mov    $0x63,%eax                 ; "c"
    82cf:	66 89 05 e6 f9 20 00 	mov    %ax,0x20f9e6(%rip)