Added support for assignments to global variables in the toplevel code

Added support for assignments to global variables in the toplevel code
generator.  We use the normal store IC mechanism with the global
object as the receiver.  The following code is generated for 'x=true'
at toplevel.

======== IA32:

27  mov eax,0xf5d06161          ;; object: 0xf5d06161 <true>
32  mov ecx,0xf5d09c35          ;; object: 0xf5d09c35 <String[1]: x>
37  push [esi+0x17]
40  call StoreIC_Initialize  (0xf5ce75c0)    ;; code: STORE_IC, UNINITIALIZED
45  mov [esp],eax

======== X64:

25  movq rax,0x7f867a7b6199    ;; object: 0x7f867a7b6199 <true>
35  movq rcx,0x7f867a7bae71    ;; object: 0x7f867a7bae71 <String[1]: x>
45  push [rsi+0x2f]
49  call StoreIC_Initialize  (0x7f8655929ac0)    ;; code: STORE_IC, UNINITIALIZED
54  movq [rsp],rax

======== ARM:

32  e59f0054       ldr r0, [pc, #+84]          ;; object: 0xf5b78161 <true>
36  e59f2054       ldr r2, [pc, #+84]          ;; object: 0xf5b7bc35 <String[1]: x>
40  e598c017       ldr ip, [r8, #+23]
44  e52dc004       str ip, [sp, #-4]!
48  e1a0e00f       mov lr, pc
52  e59ff048       ldr pc, [pc, #+72]          ;; debug: statement 0
                                               ;; code: STORE_IC, UNINITIALIZED
56  e58d0000       str r0, [sp, #+0]

Review URL: http://codereview.chromium.org/305005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3095 ce2b1a6d-e550-0410-aec6-3dcde31c8c00