* libc/include/sys/lock.h: Replaced empty {} with (0) to conform
with locking API.
* libc/include/sys/stdio.h: (_flockfile)[!_SINGLE_THREAD]: Add
check for__SSTR in _flags and if set, skip lock request.
(_funlockfile)[!SINGLE_THREAD]: Ditto.
* libc/stdio/local.h (CHECK_INIT): Added check that _REENT is
not NULL.
* libc/stdio/siprintf.c (siprintf, _siprintf_r): Added missing
initialisation of _file to -1 in local FILE.
* libc/stdio/snprintf.c (snprintf, _snprintf_r): Ditto.
* libc/stdio/sscanf.c (sscanf, _sscanf_r): Ditto.
* libc/stdio/vsnprintf.c (vsnprintf, _vsnprintf_r): Ditto.
* libc/stdio/vsscanf.c (_vsscanf_r): Ditto.
* libc/stdio/sscanf.c (sscanf, _sscanf_r): Added __SSTR flag to
_flags in local FILE to prevent locking.
* libc/stdio/vsscanf.c (_vsscanf_r): Ditto.
* libc/stdio/snprintf.c (snprintf, _snprintf_r): Fixed code
so size of 0 results in nothing being written to string.
Also fixed code so that when size is non-zero, there is only
a maximum of size - 1 characters written to the array and
a nul terminator is appended at the end.
* libc/stdio/vsnprintf.c (vsnprintf, _vsnprintf_r): Ditto.