Imported Boehm GC 5.0alpha7

[Bryce McKinlay <bryce at albatross dot co dot nz>]

I have imported the latest GC sources into libgcj. There is an important
win32 bug fix but otherwise the changes are fairly minor. Its just nice
to stay in sync with the official sources.

Since 5.0alpha6:
 - -DREDIRECT_MALLOC was broken in alpha6. Fixed.
 - Cleaned up gc_ccp.h slightly, thus also causing the HP C++ compiler
to
   accept it.
 - Removed accidental reference to dbg_mlc.c, which caused dbg_mlc.o to
be
   linked into every executable.
 - Added PREFETCH to bitmap marker.  Changed it to use the header cache.

 - GC_push_marked sometimes pushed one object too many, resulting in a
   segmentation fault in GC_mark_from_mark_stack.  This was probably an
old
   bug.  It finally showed up in gctest on win32.
 - Gc_priv.h erroneously #defined GC_incremental to be TRUE instead of
FALSE
   when SMALL_CONFIG was defined.  This was no doubt a major performance
bug for
   the default win32 configuration.
 - Removed -DSMALL_CONFIG from NT_MAKEFILE.  It seemed like an
anchronism now
   that the average PC has 64MB or so.
 - Integrated Bryce McKinley's patches for linux threads and dynamic
loading
   from the libgcj tree.  Turned on dynamic loading support for
Linux/PPC.
 - Changed the stack finding code to use environ on HP/UX.  (Thanks
   to Gustavo Rodriguez-Rivera for the suggestion.)  This should
probably
   be done on other platforms, too.  Since I can't test those, that'll
   wait until after 5.0.

regards

  [ bryce ]