Implement out-of-repo installation

[isv75]

In some environments, the system admin may require the installed files to be separate from the source code.
The added install2.sh script allows one to set the install prefix, as well as specifying per-package CMAKE_BUILD_TYPE.

I really want to use icsc at my work site, but it require some changes. The first one being to separate the binaries and the source code.

[mikhailmoiseev]

To separate sources and binaries, we are using a binary distibution which contains only required files.

The pull request contains lots of cosmetic changes which likely not required to achieve your goal. I agree to add additional installation script and minimal changes required for it. No CMakeFiles in icsc, sc_elab, sc_tools can be changed as they work in multiple environments.

[isv75]

Ok, the install script does not really depend on the other changes.

Looking into the cmake files, I notice that they depend on ENV{ICSC_HOME} in places where it would be natural to use CMAKE_CURRENT_SOURCE_DIR, for example. The cmake system keeps track of its location. Most of the "cosmetic" changes served to remove this environment dependency. The result was, in my oppinion, a more "proper" cmake configuration flow where the user is not required to source setenv.sh before building. VSCode cmake tools integration is one example.

[mikhailmoiseev]

That looks good, just a few notes:

1. Why ICSC target build in both Release and Debug mode? Does it make sense to use $CMAKE_BUILD_TYPE for ICSC?
2. Why examples build is commented? It should not take significant time, but shows the installation was successful.
3. Please update the Changelog section.

[isv75]

1. ICSC has been built in both modes by install.sh for some time (commit 12cb42b)
2. Ok
3. Ok

[mikhailmoiseev]

Thank you. Probably will move INSTALL2.md into the wiki page in some future.

[mikhailmoiseev]

Please update the install2.sh for updated version of Clang/LLVM 15.0.7. The installation procedure changed a little bit, see install.sh.

[isv75]

Updated install2.sh with LLVM (15.0.7), with upgrades to GDB and protobuf.

[mikhailmoiseev]

I do not see updated files.