fix: Remove '--enable-cgal' option incompatible with header-only

[matthewfeickert]

• Resolves CGAL explicitly requested and not found or not functional #193
• Will also fix the problem that PR build: try adding libtool to brew install  #301 is stuck on
• Reverts most of PR enabled cgal #70

---

• After FastJet's autogen.sh has been run and the configure script generated, ./configure --help shows

  --enable-cgal           enables link with the CGAL library default=no
  --enable-cgal-header-only   enable build with header-only install of CGAL, e.g. as for CGALv5; in that case do not use --enable-cgal default=no

• c.f. https://gitlab.com/fastjet/fastjet/-/tree/67796a1d43981d25a0f6d197fdfb71571028caf0

• As CGAL is a header only library there is no need to link against it or configure it and so the --enable-cgal-header-only is all that is required.
  • c.f. https://doc.cgal.org/5.6.1/Manual/usage.html#section_headeronly
• Removal of the option conflict seems to resolve multiple issues linking errors with CGAL.

[matthewfeickert]

Given #59 (comment) and checking the logs for

Configuration summary:
----------------------
  Installation directory     /home/runner/work/fastjet/fastjet/src/fastjet/_fastjet_core
  Shared libraries           yes
  Static libraries           yes
  Debug flag                 yes
  CGAL support               no
  Thread safety              yes (requires C++11)
  Plugins: EECambridge       yes
           Jade              yes
           NestedDefs        yes
           SISCone           yes
           CDFCones          yes
           D0RunICone        yes
           D0RunIICone       yes
           ATLASCone         yes
           CMSIterativeCone  yes
           PxCone            no
           TrackJet          yes
           GridJet           yes
  Monolithic plugins lib     yes
  Python interface           yes
  Swig python generator      yes
---------------------------------------------------

it seems that if this is correct that --enable-cgal-header-only is actually wrong(?). Though looking at @gavinsalam's messages in https://gitlab.com/fastjet/fastjet/-/commit/461dcecfd1b37650036f3a4931d76bd4eb4559d3

explicitly mentioned that --enable-cgal-header-only is to be used instead of --enable-cgal when using CGAL v5

this seems to contradict the configuration summary. Is it possible that the configuration summary only gives information on what is processed through the ./configure and as CGAL is header only there's nothing for it to do and so it gives

  CGAL support               no

when there is nothing wrong?

edit: Ah I see in the logs that the flag -DDROP_CGAL is getting set so it is definitely not getting used.

cc @jpivarski @lgray

[matthewfeickert]

So if you use --enable-cgal-header-only but also have no CGAL headers on the machine at all (so there's no way for it to find the headers to build) then you still get

Configuration summary:
----------------------
  Installation directory     /home/runner/work/fastjet/fastjet/src/fastjet/_fastjet_core
  Shared libraries           yes 
  Static libraries           yes 
  Debug flag                 yes 
  CGAL support               no  
  Thread safety              yes (requires C++11)
  Plugins: EECambridge       yes 
           Jade              yes          
           NestedDefs        yes          
           SISCone           yes          
           CDFCones          yes          
           D0RunICone        yes          
           D0RunIICone       yes          
           ATLASCone         yes          
           CMSIterativeCone  yes          
           PxCone            no           
           TrackJet          yes          
           GridJet           yes          
  Monolithic plugins lib     yes 
  Python interface           yes 
  Swig python generator      yes 
---------------------------------------------------

so I'm not sure how to understand the comment about using --enable-cgal-header-only with CGAL v5.