bc: replace G.eof with a special exit code of bc_vm_stdin()

function                                             old     new   delta
bc_read_line                                         305     307      +2
bc_vm_run                                            701     689     -12
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(add/remove: 0/0 grow/shrink: 1/1 up/down: 2/-12)             Total: -10 bytes

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