autosetup: keep clean the source tree on out-of-tree build

If the build host doesn't have neither jimsh nor tclsh installed,
during 'configure' the autosetup will build 'autosetup/jimsh0'
inside the source tree. This happens also when out-of-tree build
is used.
Making dirty the source tree during out-of-tree build causes
applications that use jimtcl as submodule (e.g. OpenOCD) to fail
at 'make distcheck'.

Modify 'autosetup-find-tclsh' to build 'jimsh0' in the current
folder. For jimtcl project it would be the root of the source tree
or the root of the out-of-tree build.
Update 'Makefile.in' to search for 'jimsh0' in the new path during
'distclean'.

Reported-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>