Fix printing COMPOUND_EXPR in .original [PR23872]

Fix printing COMPOUND_EXPR in .original [PR23872]

Starting with the merge of the openmp branch into the trunk
(r0-73077-g953ff28998b59b), COMPOUND_EXPR started to be printed
as `expr; , expr` which is wrong. This was due to the wrong
conversion of dumping_stmts into `!(flags & TDF_SLIM)`. That is wrong
as we are not dumping stmts at this point (`!(flags & TDF_SLIM)` was always
true for this case as TDF_SLIM case was handled before hand). So switch it
to be always false.

Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR middle-end/23872
	* tree-pretty-print.cc (dump_generic_node <case COMPOUND_EXPR>): Fix
	calls to dump_generic_node and also remove unreachable code that is testing
	`flags & TDF_SLIM`.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/atomic-21.f90: Update testcase for the removal of `;`.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>