Problems building an 8.6.0 tclkit

[cleverly-zz]

When I run:

$ mkdir 8.6 && \
tar -C 8.6 -xzvf ~/tcl8.6.0-src.tar.gz && \
mv 8.6/tcl8.6.0 8.6/tcl && \
sh config.sh 8.6/linux-ix86 thread cli && \
cd 8.6/linux-ix86 && \
make

Tcl itself builds OK but configure for the thread extension chokes (newlines added for readability) with:

checking for Tcl public headers... 
configure: error: tcl.h not found.  
Please specify its location with --with-tclinclude

Tcl itself looks fine:

$ build/bin/tclsh8.6
% info patchlevel
8.6.0
% parray tcl_platform
tcl_platform(byteOrder)     = littleEndian
tcl_platform(machine)       = x86_64
tcl_platform(os)            = Linux
tcl_platform(osVersion)     = 2.6.18-238.9.1.el5
tcl_platform(pathSeparator) = :
tcl_platform(platform)      = unix
tcl_platform(pointerSize)   = 8
tcl_platform(threaded)      = 1
tcl_platform(user)          = maclever
tcl_platform(wordSize)      = 8

If I symlink in tcl.h, tclDecls.h and tclPlatDecls.h into build/include like so:

$ cd build/include/
$ ln -s ../../../tcl/generic/tcl.h
$ ln -s ../../../tcl/generic/tclDecls.h
$ ln -s ../../../tcl/generic/tclPlatDecls.h
$ cd -

and re-run make I get a little farther; everything finishes compiling, the upx packer runs, but setupvfs.tcl fails:

./kit-cli -init- ../../setupvfs.tcl -t tclkit-cli cli
application-specific initialization failed: no files matched glob pattern "thread2*"

Suggestions?