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

Modules/Compiler/IntelLLVM.cmake

@@ -32,16 +32,16 @@ if(CMAKE_HOST_WIN32)
     else()
       set(CMAKE_${lang}_COMPILE_OPTIONS_INVALID_PCH -Winvalid-pch)
       set(CMAKE_${lang}_COMPILE_OPTIONS_WARNING_AS_ERROR "-WX")
+      if(CMAKE_${lang}_COMPILER_VERSION VERSION_GREATER_EQUAL "2021.4")
+        set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-external:I")
+        if(CMAKE_${lang}_COMPILER_VERSION VERSION_GREATER_EQUAL "2022.2")
+          set(_CMAKE_INCLUDE_SYSTEM_FLAG_${lang}_WARNING "-external:W0 ")
+        endif()
+      endif()
     endif()
     __compiler_intel_llvm_common(${lang})
     set(CMAKE_${lang}_COMPILE_OPTIONS_IPO "-Qipo")
     set(CMAKE_${lang}_LINK_OPTIONS_IPO "-Qipo")
-    if (CMAKE_${lang}_COMPILER_VERSION VERSION_GREATER_EQUAL "2021.4")
-      set(CMAKE_INCLUDE_SYSTEM_FLAG_${lang} "-external:I")
-      if (CMAKE_${lang}_COMPILER_VERSION VERSION_GREATER_EQUAL "2022.2")
-        set(_CMAKE_INCLUDE_SYSTEM_FLAG_${lang}_WARNING "-external:W0 ")
-      endif ()
-    endif ()
   endmacro()
 else()
   # GNU-like