Use libstdc++, libsupc++ and libgcc from gcc_syslibs.

* Instead of faking libstdc++.so from libstdc++.a, use libstdc++.so
  from the gcc_syslibs build feature for everything except x86_gcc2.
* Use libgcc_s.so from the gcc_syslibs build feature for everything but
  x86_gcc2 (which still carries libgcc as part of libroot.so).
* Drop filtering of libgcc objects for libroot, as that is no longer
  necessary since we're only using libgcc-as-single-object for libroot
  with x86_gcc2, where the filtered object file doesn't exist. Should
  the objects that used to be filtered cause any problems as part of
  libgcc_s.so, we can always filter them as part of the gcc build.
* Use libsupc++.so from the gcc_syslibs build feature for everything but
  x86_gcc2.
* Adjust all Jamfiles accordingly.
* Deactivate building of faked libstdc++.so for non-x86-gcc2. For
  x86_gcc2, we still build libstdc++.so from the sources in the Haiku
  source tree as part of the Haiku build .
* Put gcc_syslibs package onto the image, when needed.

src/tools/cppunit/Jamfile

@@ -49,7 +49,7 @@ SharedLibrary libcppunit.so :
 	TextTestResult.cpp
 	TypeInfoHelper.cpp
 	XmlOutputter.cpp
-	: be $(TARGET_LIBSTDC++)
+	: be [ TargetLibstdc++ ]
 ;
 
 if  $(OS) = BEOS && $(OSPLAT) != PPC {