Build gccpp library by Makefile.direct, NT_MAKEFILE and WCC_MAKEFILE

Build gccpp library by Makefile.direct, NT_MAKEFILE and WCC_MAKEFILE

* Makefile.direct: Update header comment about all, gc.a (base_lib),
c++, check, check-cpp targets.
* Makefile.direct (CXX): Refine comment.
* Makefile.direct (all): Depend also on c++.
* Makefile.direct (bsd-libgccpp.a): New target (duplicates bsd-libgc.a
one).
* Makefile.direct (bsd-libgc.a): Add a rename of gccpp.a to
bsd-libgccpp.a.
* Makefile.direct (BSD-pkg-install): Copy bsd-libgccpp.a file to
libgccpp.a, install the latter one.
* Makefile.direct (test_cpp): Depend on c++ instead of gc_cpp.o; pass
gccpp.a (instead of gc_cpp.o) to $(CXX).
* Makefile.direct (gccpp.a): New target (duplicates c++ one).
* Makefile.direct (c++): Do not depend on gc_cpp.h and base_lib;
create gccpp.a instead of updating gc.a.
* Makefile.direct (clean): Delete *.a files instead of gc.a.
* Makefile.direct (check): Depend also on test_cpp$(EXEEXT); run also
test_cpp.
* NT_MAKEFILE (LINK_GC, LINK_DLL_FLAGS): Remove variable.
* NT_MAKEFILE (OBJS): Remove gc_cpp.obj.
* NT_MAKEFILE (all, test_cpp.exe): Depend also on gccpp.lib.
* WCC_MAKEFILE (all, test_cpp.exe): Likewise.
* NT_MAKEFILE (gccpp.lib): New target (depending on gc_cpp.obj).
* WCC_MAKEFILE (gccpp.lib): Likewise.
* WCC_MAKEFILE [MAKE_AS_DLL] (gccpp.dll): Likewise.
* NT_MAKEFILE (test_cpp.exe): Pass gccpp.lib to $(link).
* WCC_MAKEFILE [MAKE_AS_LIB] (MAKE_AS_LIB): Set to -DGC_NOT_DLL.
* WCC_MAKEFILE (gc.lib): Do not depend gc_cpp.obj.
* WCC_MAKEFILE [MAKE_AS_DLL] (gc.lib): Do not add gc_cpp.obj to gc.lib.
* WCC_MAKEFILE [MAKE_AS_DLL] (gc.dll): Specify "op case".