`include-what-you-use` diagnostics, in practice, are specific to
the environment's compiler and standard library. Update includes
to satisfy IWYU for our CI job under Debian 13. Some patterns:
* Types named in virtual `override` signatures no longer require
includes since the overridden signature already names them.
* A function argument's type needs to be included even if its constructor
is called only by implicit conversion. For example, constructing a
`std::function` from a lambda now requires `<functional>`.
* Some prior mysterious `<type_traits>` inclusions are no longer required.
List of changes:
1. Remove unneeded aliases
2. Don't write VS Solution on Apple
3. Use external script to perform clean
4. Fix small bug when empty environment was
resulting in invalid file.
It greatly reduces the size of .fdb file and
makes FASTBuild run much faster in different cases.
