Enabled VPATH feature: changed nearly all Makefiles (149 files).

See sdccman.lyx '2.4.10 VPATH feature' about how to use it.

One basic decision: e.g. src/clean.mk includes further files. In order
to make this work there are two solutions:
- rename another dozen clean.mk to clean_in.mk, add srcdir to them and
  run configure on them. This way they can use
  'include $(srcdir)/port-clean.mk'
- always include clean.mk by the Makefile at the same level. To avoid
  that `make clean` tries to include and build Makefile.dep the
  MAKECMDGOALS are examined (see e.g. src/Makefile.in). This has been
  implemented, because now even `make uninstall` doesn't create
  Makefile.in. clean.mk could be eliminated by pasting it in Makefile.in.

* debugger/mcs51/Makefile.in: build own objects from library sources (SLIB, SDCC) in current directory

* configure, configure.in: renamed --disable-device-lib-build in
  --disable-device-lib; added --enable-doc, the required tools are
  searched by configure; added result message; the toolchain for the
  belonging ports are now only built, if the port is enabled.

* support/regression/*: all output is written in directory gen, because the fwk and ports directories don't livet in the build tree using vpath

* doc/sdccman.lyx: renamed --disable-device-lib-build to --disable-device-lib, added --enable-doc, added section VPATH

* sim/ucsim/configure.in,
* sim/ucsim/configure.in: hc08 couldn't be disabled, now hc08 and z80 are enabled by default

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@4121 4a8a32a2-be11-0410-ad9d-d568d2c75423