bc: partially convert lexer functions to "z" convention

bc: partially convert lexer functions to "z" convention

function                                             old     new   delta
bc_lex_token                                        1228       -   -1228
zbc_lex_token                                          -    1193   +1193
dc_lex_token                                         674       -    -674
zdc_lex_token                                          -     672    +672
bc_parse_operator                                    177       -    -177
zbc_parse_operator                                     -     175    +175
bc_parse_else                                        133       -    -133
zbc_parse_else                                         -     133    +133
bc_lex_next                                           91       -     -91
zbc_lex_next                                           -      81     +81
dc_parse_expr                                        744     748      +4
bc_parse_string                                      100     102      +2
bc_parse_body                                        114     116      +2
dc_parse_mem                                         116     115      -1
bc_parse_text                                        130     129      -1
dc_parse_register                                     51      43      -8
bc_parse_endBody                                     358     338     -20
bc_parse_name                                        513     451     -62
bc_parse_auto                                        265     201     -64
bc_parse_expr_empty_ok                              2032    1955     -77
bc_parse_parse                                       417     321     -96
bc_parse_stmt                                       1753    1598    -155
------------------------------------------------------------------------------
(add/remove: 5/5 grow/shrink: 3/9 up/down: 2262/-2787)       Total: -525 bytes
   text	   data	    bss	    dec	    hex	filename
 981975	    485	   7296	 989756	  f1a3c	busybox_old
 981450	    485	   7296	 989231	  f182f	busybox_unstripped

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