bc: convert macro bc_parse_push() to function, add debug infrastructure

bc: convert macro bc_parse_push() to function, add debug infrastructure

function                                             old     new   delta
bc_parse_push                                          -      14     +14
zbc_parse_else                                       132     134      +2
bc_parse_pushName                                     63      61      -2
zbc_parse_operator                                   174     170      -4
bc_parse_number                                       87      83      -4
zbc_parse_string                                      97      89      -8
bc_parse_pushIndex                                    68      60      -8
zbc_parse_endBody                                    339     326     -13
zbc_parse_name                                       401     387     -14
zdc_parse_mem                                        107      91     -16
zdc_parse_expr                                       680     638     -42
zbc_parse_stmt                                      1502    1456     -46
bc_parse_expr_empty_ok                              1838    1788     -50
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/11 up/down: 16/-207)         Total: -191 bytes
   text	   data	    bss	    dec	    hex	filename
 980129	    485	   7296	 987910	  f1306	busybox_old
 979938	    485	   7296	 987719	  f1247	busybox_unstripped

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