Fix Haiku/amd64 support

Fix Haiku/amd64 support
(fix of commit 847927f)

Issue #97 (bdwgc).

* include/gc_config_macros.h [__HAIKU__ && !GC_CAN_SAVE_CALL_STACKS]
(GC_ADD_CALLER): Define macro.
* include/private/gcconfig.h [__HAIKU__ && __x86_64__] (X86_64, HAIKU,
mach_type_known): Likewise.
* include/private/gcconfig.h [HAIKU && X86_64] (HEURISTIC2,
SEARCH_FOR_DATA_START): Likewise.
* include/private/gcconfig.h [UNIX_LIKE && HAIKU] (NO_GETCONTEXT):
Likewise.
* include/private/thread_local_alloc.h [GC_HAIKU_THREADS]
(USE_PTHREAD_SPECIFIC): Likewise.
* include/private/gcconfig.h [HAIKU && X86_64] (etext, DATASTART): Do
not define.