* configure.in: Update boehm-gc include dir for new GC version.
* configure: Rebuilt.
* exception.cc: Only include <gc.h>. Remove TRUE/FALSE hacks and
extern "C" wrapper.
* boehm.cc: Update includes for new GC version. MAKE_PROC is now
GC_MAKE_PROC. mark_proc is now GC_mark_proc.
* posix-threads.cc: Only include <gc.h>. Don't need to wrap with
extern "C".
From-SVN: r42380