bc: upstream fixes

bc: upstream fixes

function                                             old     new   delta
bc_parse_expr_empty_ok                              1764    1843     +79
bc_error_at                                            -      62     +62
bc_parse_inst_isLeaf                                   -      30     +30
zbc_func_insert                                      100     120     +20
bc_error_bad_function_definition                       -      10     +10
bc_error_bad_assignment                                -      10     +10
zxc_lex_next                                        1608    1614      +6
ok_in_expr                                            30       -     -30
zxc_vm_process                                       874     839     -35
------------------------------------------------------------------------------
(add/remove: 4/1 grow/shrink: 3/1 up/down: 217/-65)           Total: 152 bytes

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