Code refactoring of huge_test

Code refactoring of huge_test

* tests/huge_test.c [!GC_MAXIMUM_HEAP_SIZE] (GC_MAXIMUM_HEAP_SIZE,
GC_INITIAL_HEAP_SIZE): Define (before include gc.h); move the comment
from main().
* tests/huge_test.c (CHECK_ALLOC_FAILED): New macro.
* tests/huge_test.c (main): Remove "r" local variable; do not call
GC_set_max_heap_size and GC_expand_hp explicitly (as it is done
by GC_INIT provided GC_MAXIMUM_HEAP_SIZE and GC_INITIAL_HEAP_SIZE are
defined); use CHECK_ALLOC_FAILED (instead of if/fprintf/exit).