Do not call GC_dirty_inner unless GC_incremental

Do not call GC_dirty_inner unless GC_incremental
(a cherry-pick of commits bb8e97c1, f30c0150 from 'master')

* include/private/gc_priv.h [MANUAL_VDB] (GC_dirty_inner):
Declare GC_INNER function.
* include/private/gc_priv.h (GC_dirty): Define macro (calls
GC_dirty_inner if MANUAL_VDB and GC_incremental.
* mallocx.c [MANUAL_VDB] (GC_dirty): Remove declaration.
* mark.c [MANUAL_VDB && THREADS] (GC_dirty): Likewise.
* stubborn.c [MANUAL_VDB] (GC_dirty): Likewise.
* os_dep.c [MANUAL_VDB] (GC_dirty): Rename to GC_dirty_inner;
add GC_INNER; change argument type from ptr_t to const void*.