Stack overflow in CMake 3.11.0 GUI on osx/linux

See also #17659 (closed) for a related issue and for instructions how to reproduce this crash. The root cause for both issues is the ancient regex implementation (see also #17686).

The CMake console application is not affected by this crash. However, the GUI application crashes on osx (and probably on linux as well) due to insufficient stack space. It seems that the main thread has 8MB stack space per default whereas helper threads only get 512KB (depending on the threading API used). The regex code is run in a helper thread and produces a stack overflow.

Windows builds are not affected by this problem since !1728 (merged).