* 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.
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