Replace GC_DBG_RA with GC_DBG_EXTRAS macro

Replace GC_DBG_RA with GC_DBG_EXTRAS macro

* dbg_mlc.c (GC_debug_malloc_replacement,
GC_debug_realloc_replacement): Use GC_DBG_EXTRAS (instead of
"GC_DBG_RA NULL, 0").
* malloc.c (GC_debug_malloc_replacement): Likewise.
* mallocx.c (GC_debug_realloc_replacement): Likewise.
* include/private/gc_priv.h (GC_DBG_EXTRAS): New macro (similar to
GC_EXTRAS but pass NULL/0 instead of __FILE__and __LINE__);
pass "unknown" instead of NULL unless GC_ADD_CALLER.
* include/private/gc_priv.h (GC_DBG_RA): Remove.