bc: stop passing around pointers to G.prog, they are all constant

bc: stop passing around pointers to G.prog, they are all constant

function                                             old     new   delta
bc_program_exec                                     4523    4562     +39
bc_program_assign                                    450     482     +32
bc_program_assignStr                                 131     159     +28
bc_program_print                                     762     775     +13
bc_program_num                                      1134    1147     +13
bc_program_search                                    154     164     +10
bc_num_ulong                                          85      95     +10
dc_parse_expr                                        719     727      +8
bc_program_retire                                     34      40      +6
bc_program_reset                                     168     174      +6
bc_program_binOpRetire                                50      56      +6
bc_program_addFunc                                   220     226      +6
bc_program_prep                                       88      89      +1
dc_parse_init                                         18      17      -1
bc_program_copyToVar                                 355     354      -1
bc_parse_text                                        142     141      -1
bc_parse_number                                       88      87      -1
bc_parse_init                                         18      17      -1
bc_parse_endBody                                     423     422      -1
common_parse_init                                     29      26      -3
bc_parse_string                                      103     100      -3
bc_parse_addFunc                                      44      41      -3
bc_program_call                                      371     366      -5
bc_program_binOpPrep                                 301     296      -5
bc_program_read                                      342     336      -6
bc_parse_create                                      198     192      -6
bc_program_pushArray                                 143     136      -7
bc_parse_reset                                       194     187      -7
bc_vm_process                                        323     315      -8
bc_program_pushVar                                   236     225     -11
bc_vm_run                                           1872    1854     -18
bc_parse_name                                        590     570     -20
bc_program_execStr                                   594     573     -21
bc_program_modexp                                    793     763     -30
bc_program_printStream                               172       -    -172
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 13/21 up/down: 178/-331)       Total: -153 bytes
   text	   data	    bss	    dec	    hex	filename
 988728	    485	   7296	 996509	  f349d	busybox_old
 988575	    485	   7296	 996356	  f3404	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>