problem with TCLSH when reconfiguring LLVM (was Re: make TEST=ipodbgopt in sqlite3: problem with TCLSH)

Doesn't the toplevel configure set TCLSH in Makefile.config?

There seems to be a problem with reconfiguring LLVM when you use a
config.cache file. In an empty directory I get:

$ ~/svn/llvm-project/llvm/trunk/configure --cache-file=config.cache
[... lots of stuff ...]
$ grep -i tclsh Makefile.config
TCLSH := /usr/bin/tclsh8.4
$ ~/svn/llvm-project/llvm/trunk/configure --cache-file=config.cache
[... lots of stuff ...]
$ grep -i tclsh Makefile.config
TCLSH :=

So the second time I configure, something in config.cache is
scuppering configure's attempt to find tclsh. This seems bad. Can
anyone who know about autoconf explain this? My config.cache contains
these lines:

ac_cv_path_TCLSH=${ac_cv_path_TCLSH=/usr/bin/tclsh8.4}
ac_cv_path_tclsh=${ac_cv_path_tclsh=/usr/bin/tclsh8.4}

Thanks,
Jay.