c: Implement C2Y complex increment/decrement support

Support for complex increment and decrement (previously supported as
an extension) was voted into C2Y today (paper N3259).  Thus, change
the pedwarn to a pedwarn_c23 and add associated tests.

Note: the type of the 1 to be added / subtracted is underspecified (to
be addressed in a subsequent paper), but understood to be intended to
be a real type (so the sign of a zero imaginary part is never changed)
and this is what is implemented; the tests added include verifying
that there is no undesired change to the sign of a zero imaginary
part.

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc/c/
	* c-typeck.cc (build_unary_op): Use pedwarn_c23 for complex
	increment and decrement.

gcc/testsuite/
	* gcc.dg/c23-complex-1.c, gcc.dg/c23-complex-2.c,
	gcc.dg/c23-complex-3.c, gcc.dg/c23-complex-4.c,
	gcc.dg/c2y-complex-1.c, gcc.dg/c2y-complex-2.c: New tests.

0 files changed, 0 insertions, 0 deletions