Fix compile failures

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
libbb: make rtc_xopen try harder on EBUSY

function                                             old     new   delta
rtc_xopen                                             77     139     +62

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
libbb: fix thinko in rtc_xopen()

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
rtcwake: fix incorrect (reversed) rtc/sys adjuestment; code shrink

function                                             old     new   delta
rtcwake_main                                         482     462     -20

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
libbb: fix empty PATH components handling

function                                             old     new   delta
find_execable                                         81      86      +5
exists_execable                                       71      66      -5

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
libbb: rename execable -> executable. No code changes

English speakers complained that it sounded awfully broken.

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