Remove references to old missing gc_alloc.h and gc_local_alloc.h files.

Remove references to old missing gc_alloc.h and gc_local_alloc.h files.
Remove unused HPUX GC_test_and_clear implementation.

* hpux_test_and_clear.s: Remove.
* Makefile.am (EXTRA_DIST): Remove hpux_test_and_clear.s.
* Makefile.direct (SRCS): Ditto.
* Makefile.dj (SRCS): Ditto.
* Makefile.dj (SRCS): Remove missing gcc_support.c,
include/gc_alloc.h, include/gc_local_alloc.h.
* doc/gcdescr.html: Remove information about gc_local_alloc.h.
* doc/gcinterface.html: Ditto.
* doc/scale.html: Ditto.
* doc/gcinterface.html: Remove information about gc_alloc.h.
* tests/test_cpp.cc: Don't include missing old gc_alloc.h (include
new_gc_alloc.h instead); don't test __GNUC__.
* tests/test_cpp.cc (main): Use gc_alloc class instead of alloc (don't
test __GNUC__).
* windows-untested/vc60/gc.dsp (SOURCE): Don't include missing
gc_alloc.h, gc_local_alloc.h.
* windows-untested/vc60/libgc.dsp (SOURCE): Ditto.
* windows-untested/vc70/gc.vcproj (Header Files): Ditto.
* windows-untested/vc70/libgc.vcproj (Header Files): Ditto.
* windows-untested/vc71/gc.vcproj (Header Files): Ditto.
* windows-untested/vc71/libgc.vcproj (Header Files): Ditto.