v4: Update ifx flags for avx2

[mathomp4]

This pull request updates the Intel LLVM Fortran flags to use -march=x86-64-v3 instead of -march=core-avx2 for better compatibility and performance. The changes affect the CHANGELOG.md and compiler/flags/IntelLLVM_Fortran.cmake files.

Intel LLVM Fortran Flags Update:

• CHANGELOG.md: Added an entry to reflect the update of Intel LLVM Fortran flags to use -march=x86-64-v3 instead of -march=core-avx2.

• compiler/flags/IntelLLVM_Fortran.cmake:

  • Replaced COREAVX2_FLAG with MARCH_FLAG and updated its value to -march=x86-64-v3 for AMD, Hygon, and Intel processors.
  • Updated GEOS_Fortran_Vect_Flags to use the new MARCH_FLAG instead of COREAVX2_FLAG.
  • Updated GEOS_Fortran_Aggressive_Flags to use the new MARCH_FLAG instead of COREAVX2_FLAG.