ASM: Loading address of label truncates to 32 bits on x64

[claptrap]

```d
asm
{
         mov EAX,idx;
         shl EAX,4;
         lea RCX,LOOKUP;
         jmp [RCX+RAX];
LOOKUP:
         lea R9,CASE0;
         jmp ENDLOOKUP;
         align 16;
         lea R9,CASE1;
         jmp ENDLOOKUP;
         align 16;
ENDLOOKUP:

}

00007FF760D244A7  mov         eax,dword ptr [rbp-48h]
00007FF760D244AA  shl         eax,4
00007FF760D244AD  lea         rcx,[60D244B8h]
00007FF760D244B5  jmp         qword ptr [rcx+rax]
00007FF760D244B8  lea         r9,[60D24572h]
00007FF760D244C0  jmp         00007FF760D244E0
00007FF760D244C2  nop         word ptr cs:[rax+rax]
00007FF760D244D0  lea         r9,[60D2455Bh]
00007FF760D244D8  jmp         00007FF760D244E0
```

All the "lea REG,label" instructions are missing the top 32 bits 
of the actual address.

Looks like a bug to me as it works OK on DMD. At least I compiled 
a small test and DMD prints out a 64 bit address