In Debian, tclConfig.sh installs into with a symlink in for a default version. However, the default version symlink is present only if tcl-dev package is installed, while tcl8.* packages don't install it themselves.

It'd be cool if tcl.m4 checked those per-version locations too:

<verbatim>
--- a/tcl.m4
+++ b/tcl.m4
@@ -138,6 +138,7 @@
 			`ls -d \
 			`ls -d \
 			`ls -d \
+			`ls -d \
 			; do
 		    if test -f "$i/tclConfig.sh" ; then
 			ac_cv_c_tclconfig="`(cd $i; pwd)`"
</verbatim>