[LTP] Sparse checks does not include other headers in include

[Petr Vorel]

Hi Richie,

cd lib && make check-tst_device

...
tst_device.c:78:5: warning: Symbol 'tst_find_free_loopdev' has no prototype or library ('tst_') prefix. Should it be static?
tst_find_free_loopdev() is in include/tst_device.h. Could sparse-ltp.c take into
consideration all files in include/ (if is trivial to do that)?

Kind regards,
Petr