system-tclpath: fix package build and nf.EMC2_TCL_DIR

- nf.py.in: expose EMC2_TCL_DIR so rs274/options.py can read it
  (fixes 'module nf has no attribute EMC2_TCL_DIR' at runtime)
- control.top.in: build-depend on tcl for /usr/bin/tclsh; src/configure
  queries tcl_pkgPath in override_dh_auto_configure, which runs after
  build-deps, so no bootstrap issue
- configure.ac: stop the install branch from clobbering EMC2_TCL_DIR set
  by --with-tcl-dir

Author: grandixximo

debian/control.top.in

@@ -42,6 +42,7 @@ Build-Depends:
     python3-dev,
     python3-tk,
     python3-xlib,
+    tcl,
     tcl@TCLTK_VERSION@-dev,
     tclx,
     tk@TCLTK_VERSION@-dev,

lib/python/nf.py.in

@@ -105,6 +105,7 @@ def find_prefix(f):
     return find_prefix(os.path.dirname(f))
 
 PREFIX = "@prefix@"
+EMC2_TCL_DIR = "@EMC2_TCL_DIR@"
 SHARE = os.path.join(PREFIX, "share", "axis")
 tcl_libdir = os.path.join(SHARE, "tcl")
 

src/configure.ac

@@ -735,7 +735,6 @@ else
     EMC2_SCRIPT=$EMC2_BIN_DIR/linuxcnc
     EMC2_SUFFIX=""
     EMC2_ICON=linuxcncicon
-    EMC2_TCL_DIR="${TCL_GET_DIR}/linuxcnc"
     EMC2_TCL_LIB_DIR="${EMC2_TCL_DIR}"
     EMC2_LANG_DIR="${EMC2_TCL_DIR}/msgs"
     EMC2_PO_DIR=${prefix}/share/locale