include the missing cpp2regex.h in cpp2util target

[mantkiew]

Currently, the required cpp2regex.h is not getting installed and the example cannot be built.

Changes:

• include cpp2regex.h for the target cpp2util.
• update cppfront submodule to v0.7.2

Tested on Ubuntu 24.04 with cmake 3.30.1.

[alexreinking]

This change is incorporated in #165 already -- but there's a test failure I didn't have a chance to diagnose. Do you know anything about that?

[mantkiew]

@alexreinking Trying here with the official 0.7.2 release commit for the submodule instead of the latest main, which is WIP and often broken. Also, I ran with Clang 18.1.3 on Ubuntu 24.04 and it works now. There were some issues with Clang 18.1.1 before.

[alexreinking]

Oh, he's doing actual releases now? That works for me.

[alexreinking]

I'm going to start from here and try to fix the tests. Thanks for helping out!