The MSVC makefiles for regex (libs/regex/build) create 1_40 filenames. I assume (at least) one of:

- they missed the update.

Yep, my bad. Forgot all about them :-(

- they're obsolete; just use bjam.

Also true.

- I've missed something.

Nope. My mistake, a quick search and replace in the makefile would fix the issue though... HTH, John.