Small optimization in signal and ioctl tables

Small optimization in signal and ioctl tables

Trivial shuffling of data tables puts them all in one file,
allowing gcc to see their sizes and eliminate variables
which store these sizes.

Surprisingly, in C mode gcc does not optimize out static const int
variables. Help it by using enums instead.

* defs.h: Stop exporting ioctlent{0,1,2}, nioctlents{0,1,2},
signalent{0,1,2}, nsignals{0,1,2}.
* ioctl.c: Remove definitions of ioctlent{,0,1,2} and nioctlents{,0,1,2}.
* signal.c: Remove definitions of signalent{,0,1,2} and nsignals{,0,1,2}.
* syscall.c: Move above definitions to this file. Make them static const
or enums if suitable.