[match.pd] Handle abs pattern with convert

gcc/ChangeLog:

	* match.pd: Extend A CMP 0 ? A : -A into (type)A CMP 0 ? A : -A.
	Extend A CMP 0 ? A : -A into (type) A CMP 0 ? A : -A.

gcc/testsuite/ChangeLog:

	* g++.dg/absvect.C: New test.
	* gcc.dg/tree-ssa/absfloat16.c: New test.

Signed-off-by: Kugan Vivekanandarajah <kvivekananda@nvidia.com>