[WIP] Drop the need for exporting TCLLIBPATH, use system path [v2]

[NTULINUX]

I don't know how to restore my last PR properly with the fixed tree so making a new one.

This avoids hard-coding LinuxCNC to use a path outside of the system's default Tcl search path, making it no longer required to specify TCLLIBPATH on Gentoo and Fedora. Logging in and out in order to update the environmental variables so the icons/menu entries work is also no longer needed.

[NTULINUX]

@BsAtHome do you have any recommendations on fixing linuxcnc.install.in so it uses EMC2_TCL_DIR instead of hard-coding it to usr/lib/tcltk? I can add it to configure.ac but I don't think that's right.

What about something like:

diff --git a/debian/configure b/debian/configure
index 096b3f4a5e..f715227ec8 100755
--- a/debian/configure
+++ b/debian/configure
@@ -152,6 +152,8 @@ KERNEL_DEPENDS_BUILD=libudev-dev
 KERNEL_HEADERS=
 KERNEL_VERSION=uspace
 MODUTILS_DEPENDS=
+TCL_GET_DIR=$(echo 'puts [tcl::pkgconfig get scriptdir,runtime]' | tclsh)
+EMC2_TCL_DIR="${TCL_GET_DIR}/linuxcnc"
 if false; then
 MAIN_PACKAGE_NAME=linuxcnc
 OTHER_MAIN_PACKAGE_NAME=linuxcnc-uspace
@@ -177,6 +179,7 @@ sed \
     -e "s#@KERNEL_HEADERS@#$KERNEL_HEADERS#g" \
     -e "s#@KERNEL_VERSION@#$KERNEL_VERSION#g" \
     -e "s#@LIBREADLINE_DEV@#$LIBREADLINE_DEV#g" \
+    -e "s#@EMC2_TCL_DIR@#$EMC2_TCL_DIR#g" \
     -e "s#@MAIN_PACKAGE_NAME@#$MAIN_PACKAGE_NAME#g" \
     -e "s#@MODULE_EXT@#$MODULE_EXT#g" \
     -e "s#@MODULE_PATH@#$MODULE_PATH#g" \

There's also this hard-code too in rules.in:

	if [ -x  "$(DESTDIR)/usr/lib/tcltk/linuxcnc/linuxcnc.tcl" ]; then \
		chmod -x $(DESTDIR)/usr/lib/tcltk/linuxcnc/linuxcnc.tcl; \
	fi

Trying something...

[NTULINUX]

Uh oh.. build failed:

debian/configure: line 155: tclsh: command not found

Adding tcl to .github/scripts/install-deps.sh doesn't work..