build(cmake): fix compiler detection logic

[e-kwsm]

the condition wrongly matched LLVMFlang (flang-new), which does not support -Mbackslash and -Mallocatable=03.

https://cmake.org/cmake/help/v3.24/variable/CMAKE_LANG_COMPILER_ID.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.78%. Comparing base (77f65c6) to head (5c0001d).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #70      +/-   ##
==========================================
- Coverage   69.79%   69.78%   -0.01%     
==========================================
  Files          64       64              
  Lines        8618     8639      +21     
  Branches     2579     2586       +7     
==========================================
+ Hits         6015     6029      +14     
- Misses        782      783       +1     
- Partials     1821     1827       +6     

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[e-kwsm]

-Mbackslash corresponds to -fno-backslash (default) in LLVMFlang, but I am not sure what is the counterpart of -Mallocatable=03.

Note that flang-new 18.1.8 does not compile MCTC because it does not support polymorphic types yet.

[ajmay81]

I've also just come across this after trying to update to the very latest dftd4.

-Mbackslash corresponds to -fno-backslash (default) in LLVMFlang, but I am not sure what is the counterpart of -Mallocatable=03.

Yes, those options are not needed/default with flang-new.

Note that flang-new 18.1.8 does not compile MCTC because it does not support polymorphic types yet.

It was building fine with flang-new built from their main branch:

-- The Fortran compiler identification is LLVMFlang 20.0.0

One has to add -DCMAKE_Fortran_FLAGS_RELEASE='-mmlir -allow-assumed-rank to get the experimental assumed rank implementation, but it seems to work fine. Note, one should not include this option in any cmake files since it will (hopefully) soon enough become enabled by default.

[awvwgk]

Good catch thanks for sharing