tcl: fix tclConfig.sh to point to the correct private headers

When building expect with rm_work enabled, it was not finding the correct private
header files because they were removed from the WORKDIR, this fixes the tclConfig.sh
to point to the sysroot private area instead.

This also fixes the -L directory to point to STAGING_LIBDIR instead if INCDIR!

[YOCTO #5620]

Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>