Support IntelLLVM compiler

[DusanJovic-NOAA]

Description

This PR adds support for Intel LLVM compiler.

Changes:

• CMakeLists.txt is updated to recognize 'IntelLLVM' compiler id as an Intel compiler.
• Added cmake/compiler_flags_IntelLLVM_Fortran.cmake and cmake/fv3_compiler_flags.cmake to define Intel LLVM compiler flags
• Add special case for IntelLLVM compiler in driver/fvGFS/atmosphere.F90 to read namelist from a file instead from a character variable to avoid internal compiler error.

Fixes # (issue)

How Has This Been Tested?

ufs-weather-model regression test has been run on Hera. See https://github.com/ufs-community/ufs-weather-model/pull/2224

Checklist:

Please check all whether they apply or not

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] Any dependent changes have been merged and published in downstream modules