[CMake]Allow user specified CPack Options

[Naville]

Summary

This should allow downstream vendors to install multiple LLVM distributions in parallel.

Should we also patch the default values to allow multiple upstream llvm distribution?

[Naville]

This patch deserves a FAQ so here we are:

• Won't this break MSVC?
• MSVC uses the one in `VS\2019\Professional\VC\Tools\LLVM` unless you manually override the *.prop settings

[thieta]

I am fine with the user-overridable variables. I am not sure about switching the install root - It would be fine to have LLVM/15.0.0 and LLVM/16.0.0 for example. But not sure if there is any big issues with switching the directory at this time. For our internal distribution we don't use this installer so it doesn't matter that much for me.

Let's wait for input from @hans and @pbo-linaro

[pbo-linaro]

The idea is nice. Should we allow user to override all this, or simply change default to LLVM/$version instead?

I have no clue if this would break anything with MSVC, why would it be a problem?
It's already possible to extract installer content (using 7z for instance), and relocate it without problem, so I don't expect changing install path would break something.

[hans]

Allowing developers to override the variables sgtm.

I'm not sure about changing the default dir. Is it a common use case to have multiple versions installed? Users who want to can already select a different dir when installing. Also I think the installer will bring up a "Do you want to uninstall the old version before installing the new one", even if the install dir is changed. Having a default install dir without the version also makes it a little easier for simple scripts to find it.

But overall I don't feel strongly about this. Changing the dir probably shouldn't break anything, but I also don't know if there are real benefits?

[thieta]

Yeah I think I am on the same page as Hans here - let's make it overrideable but let's not change the default dir - it can already be changed by the user.

[Naville]

@pbo-linaro

Simply change default to LLVM/$version instead?

This stops downstream vendors (myself included) from distributing their own fork and install side-by-side with LLVM official releases, which kinda defeats the purpose

@hans

Is it a common use case to have multiple versions installed

Many downstream vendors do, like Swift install a separate LLVM toolchain on macOS with each release, same applies for Windows at least for our company, due to sometimes compiler regressions and whatnot

Also I think the installer will bring up a "Do you want to uninstall the old version before installing the new one"

Don't think this is the case as long as CPACK_PACKAGE_INSTALL_REGISTRY_KEY is changed as well

Having a default install dir without the version also makes it a little easier for simple scripts to find it.

For windows I think it's also stored in system registry

@thieta

let's make it overrideable but let's not change the default dir - it can already be changed by the user.

Very fair point, hence this diff currently doesnt change the defaults

[pbo-linaro]

Considering that use case, then it seems to be the best approach. lgtm

llvm/CMakeLists.txt

 set(PACKAGE_NAME LLVM)
 set(PACKAGE_STRING "${PACKAGE_NAME} ${PACKAGE_VERSION}")
 set(PACKAGE_BUGREPORT "https://github.com/llvm/llvm-project/issues/")
 
 set(BUG_REPORT_URL "${PACKAGE_BUGREPORT}" CACHE STRING
   "Default URL where bug reports are to be submitted.")
 
 # Configure CPack.
+if(NOT DEFINED CPACK_PACKAGE_INSTALL_DIRECTORY)
   set(CPACK_PACKAGE_INSTALL_DIRECTORY "LLVM")
+endif()
+if(NOT DEFINED CPACK_PACKAGE_VENDOR)
   set(CPACK_PACKAGE_VENDOR "LLVM")
+endif()
 set(CPACK_PACKAGE_VERSION_MAJOR ${LLVM_VERSION_MAJOR})
 set(CPACK_PACKAGE_VERSION_MINOR ${LLVM_VERSION_MINOR})
 set(CPACK_PACKAGE_VERSION_PATCH ${LLVM_VERSION_PATCH})
 set(CPACK_PACKAGE_VERSION ${PACKAGE_VERSION})
 set(CPACK_RESOURCE_FILE_LICENSE "${CMAKE_CURRENT_SOURCE_DIR}/LICENSE.TXT")
-set(CPACK_NSIS_COMPRESSOR "/SOLID lzma \r\n SetCompressorDictSize 32")
 if(WIN32 AND NOT UNIX)
+  set(CPACK_NSIS_COMPRESSOR "/SOLID lzma \r\n SetCompressorDictSize 32")
+  if(NOT DEFINED CPACK_PACKAGE_INSTALL_REGISTRY_KEY)
     set(CPACK_PACKAGE_INSTALL_REGISTRY_KEY "LLVM")
+  endif()
   set(CPACK_PACKAGE_ICON "${CMAKE_CURRENT_SOURCE_DIR}\\\\cmake\\\\nsis_logo.bmp")
   set(CPACK_NSIS_MUI_ICON "${CMAKE_CURRENT_SOURCE_DIR}\\\\cmake\\\\nsis_icon.ico")
   set(CPACK_NSIS_MUI_UNIICON "${CMAKE_CURRENT_SOURCE_DIR}\\\\cmake\\\\nsis_icon.ico")
   set(CPACK_NSIS_MODIFY_PATH "ON")
   set(CPACK_NSIS_ENABLE_UNINSTALL_BEFORE_INSTALL "ON")
   if( CMAKE_CL_64 )
+    if(NOT DEFINED CPACK_NSIS_INSTALL_ROOT)
       set(CPACK_NSIS_INSTALL_ROOT "$PROGRAMFILES64")
     endif()
   endif()
+endif()
 include(CPack)
 
 # Sanity check our source directory to make sure that we are not trying to
 # generate an in-source build (unless on MSVC_IDE, where it is ok), and to make
 # sure that we don't have any stray generated files lying around in the tree
 # (which would end up getting picked up by header search, instead of the correct
 # versions).
 if( CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR AND NOT MSVC_IDE )