Refactoring in commit v3.4.0-rc1~321^2 (cmMakefile: Remove special
handling of INCLUDE_REGULAR_EXPRESSION, 2015-04-04) accidentally broke
propagation of the include regex to subdirectories. Refactoring in
commit v3.5.0-rc1~319^2~1 (cmState: Initialize properties immediately,
2015-10-07) moved maintenance of this value from `cmMakefile` to
`cmStateSnapshot`.
Restore propagation of the `INCLUDE_REGULAR_EXPRESSION` to
subdirectories and add a test to cover it.
Fixes: #17676
In commit 0bbd993f (Make CMAKE_HOST_SYSTEM_NAME available in scripting
context, 2016-12-26) we added a call to `uname` that checks for a zero
return value. However, on Solaris the `uname(2)` manual [1] says that
on success a non-negative value is returned. Fix our return code check
so that we detect the `SunOS` name correctly.
[1] https://docs.oracle.com/cd/E53394_01/html/E54765/uname-2.html
Port dependents to the new locations as needed.
Leave behind a cmState.h include in cmListFileCache to reduce noise. It
is removed in a following commit.
