genconditions: Add support for targets without non-trivial insn conditions

genconditions: Add support for targets without non-trivial insn conditions

Somebody complained on IRC that when writing a new backend one can get
an error while compiling build/gencondmd.cc.
The problem is that when host compiler is g++ 3 or later (or when
bootstrapping), we compile it with g++ -std=c++11 -pedantic and
the generated insn_conditions array contains pairs
{ "cond", __builtin_constant_p (cond) ? (int) (cond) : -1 },
where cond is some non-trivial instruction condition.  Now if a target
uses "" for all the conditions (admittedly unlikely for non-trivial
target), the initializer for insn_conditions[] is {} and that is
pedantically rejected because C++ doesn't support zero-sized arrays.

The following patch fixes that by adding an artificial termination
element and skips that during the walk.

2022-05-04  Jakub Jelinek  <jakub@redhat.com>

	* genconditions.cc (write_conditions): Append a { nullptr, -1 }
	element at the end of insn_conditions.
	(write_writer): Use ARRAY_SIZE (insn_conditions) - 1 instead of
	ARRAY_SIZE (insn_conditions).