When CMAKE_FASTBUILD_USE_RELATIVE_PATHS is set -
use relative paths for Unity nodes as well as for include directories.
It makes it possible to share cache across different location of
the same repo (or potentially across different machines)
Right now, all IDE projects are located at the top level which makes it pretty messy when there are a lot of them.
With this change the generated IDE project will more closely mimic existing folder structure in the project.
Two optimizations here:
1. Remove non-mandatory aliases (I only used them for debugging).
2. Make objects lists' name shorter
Both of those improvements contribute to the decrease of the FASTBuild DB file, since they are getting serialized.
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.
Compilation is complicated. Caching / distribution is even more
complicated. Sometimes there are bugs (in compilers as well as in
FASTBuild), so export the option to disable those features for CMake
targets.
