For 'OMP_CLAUSE' in 'dump_generic_node', dump the whole OMP clause chain

For 'OMP_CLAUSE' in 'dump_generic_node', dump the whole OMP clause chain

... instead of just the first clause.

	gcc/
	* tree-pretty-print.h (dump_omp_clauses): Add 'bool = true'
	default argument.
	* tree-pretty-print.c (dump_omp_clauses): Update.
	(dump_generic_node) <OMP_CLAUSE>: Use it.
	gcc/testsuite/
	* gcc.dg/gomp/simd-clones-2.c: Enhance.

(cherry picked from commit 2973090c4c62105cbb61bfc6f83be903e3c46c71)