IntelLLVM: Revert accidental use of -external:I with Fortran compilers In commit 8218aed118 (IntelLLVM: support marking include paths as SYSTEM directories, 2023-08-15, v3.29.0-rc1~81^2) this flag was added for the C and C++ compilers, but was accidentally added for Fortran too. Remove it for the latter, as it is unsupported. Issue: #25807