csp_error: Add CSP_ERR_NOSYS for unimplemented functions
csp_error: Add CSP_ERR_NOSYS for unimplemented functions

This commit adds CSP_ERR_NOSYS with the value 38.  This error number
is taken from POSIX.1-2001 ENOSYS.  Depending on CSP_HAVE_STDIO, some
functions won't be included in libcsp.  In that case, the functions
should return -ENOSYS.

Signed-off-by: Yasushi SHOJI <afa9ca3be149447780c2f7b524d61ed3d3db63f9@spacecubics.com>

libcsp/libcsp,libcsp/libcsp