FindTCL: Find 8.6 libraries with 't' suffix
Building Tcl with makefile.vc
produces library files with a t
suffix to indicate threading support. Since threading support is
on by default in 8.6 anyway, the libraries should be compatible.
Issue: https://github.com/conda-forge/tk-feedstock/issues/12
Topic-rename: FindTCL-thread-suffix
Edited by Brad King