Fix a crash due to mismatch of free and GOMP_alloc.

Fix a crash due to mismatch of free and GOMP_alloc.

With allocate directive, we replace the malloc calls to GOMP_alloc if
it is associated with the allocate statement.  The memory was supposed
to be free-d by the implicitely generated free calls which also get
replaced.  But if user explicitely deallocated the memory using the
deallocate statement, it can cause a mismatch.  This commit handles
that case and also replaces the free call generated for deallocate
clause.

Also added deallocate in the testcase and tidied it up a bit.

gcc/ChangeLog.omp:

	* omp-low.c (lower_omp_allocate): Move allocate declaration
	inside loop.  Set it to false at the end of condition.

libgomp/ChangeLog.omp:
	* testsuite/libgomp.fortran/allocate-2.f90: Remove commented lines.
	Add deallocate.  Remove omp_atk_pool_size trait.