bc: propagate fixed arguments into callees

bc: propagate fixed arguments into callees

Looks like there is only one "BcProgram" object, &G.prog.

function                                             old     new   delta
bc_program_exec                                     4401    4523    +122
bc_program_execStr                                   579     606     +27
bc_program_read                                      323     342     +19
bc_args                                               83      97     +14
bc_vm_process                                        327     323      -4
bc_num_ulong                                          95      85     -10
dc_main                                               62      48     -14
bc_main                                               62      48     -14
bc_vm_run                                           2317    1923    -394
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/5 up/down: 182/-436)         Total: -254 bytes
   text	   data	    bss	    dec	    hex	filename
 989028	    485	   7296	 996809	  f35c9	busybox_old
 988774	    485	   7296	 996555	  f34cb	busybox_unstripped

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