How to build
./configure --prefix=/c/bin/tcl8.6.9 --with-tcl=/c/src/tcl8.6.9/win --with-tk=/c/src/tk8.6.9/win --enable-threads CPPFLAGS=-static make install
./configure --prefix=/c/bin/tcl8.6.9-x64 --with-tcl=/c/src/tcl8.6.9-x64/win --with-tk=/c/src/tk8.6.9-x64/win --enable-threads --enable-64bit CPPFLAGS=-static make install
I needed to delete the following files in MSYS2 in order to remove the dependency on MinGW DLLs. CPPFLAGS="-static" was not enough.
Tcl patchlevel insensitive patch
TkBLT is a stab-enabled package but it works with the exact patchlevel at which it was built. I used Tcl/Tk 8.6.8. So it can't be used in 8.6.7 or 8.6.9. I found a workaround. Note that it might be against author's intention.