Add the "Intel Compiler Support" section to discuss classic and oneAPI

support.

src/doc/ESMF_install.tex

@@ -1111,6 +1111,37 @@ \subsection{Supported Platforms}
 will be stored in a separate directories so the results will be kept
 separate for different architectures or options.
 
+\subsubsection{Intel Compiler Support (Classic and oneAPI)}
+
+ESMF supports the Intel compiler suite via {\tt ESMF\_COMPILER=intel}. Starting in 2020, Intel began promoting their
+new LLVM-based C/C++ and Fortran compiler line under the oneAPI brand. As of 2023, the older compilers are still
+part of the Intel compiler suite and referred to as Intel Compiler Classic. ESMF supports both the classic and oneAPI
+compiler lines. The following paragraphs povide important details that allow users to fine-tune the interaction
+with the Intel compilers.
+
+Under {\tt ESMF\_OS=Linux}, with {\tt ESMF\_COMPILER=intel} and {\tt ESMF\_COMM=mpiuni} set, the C, C++, and
+Fortran compiler front-ends default to the classic options {\tt icc}, {\tt icpc}, and {\tt ifort}, respectively. Any
+of these defaults can be overridden by explicitly setting the {\tt ESMF\_C}, {\tt ESMF\_CXX}, or {\tt ESMF\_F90}
+environment variables to the oneAPI options {\tt icx}, {\tt icpx}, and {\tt ifx}, respectively.
+
+Under {\tt ESMF\_OS=Linux}, with {\tt ESMF\_COMPILER=intel} and {\tt ESMF\_COMM=intelmpi} set, the C, C++, and
+Fortran compiler front-ends default to the MPI compiler wrappers {\tt mpiicc}, {\tt mpicpc}, and {\tt mpiifort},
+respectively. It depends on the IntelMPI installation details whether classic, oneAPI, or a mixture of compilers
+are used underneath the MPI wrappers. The IntelMPI defaults can be overridden by explicitly setting the
+{\tt I\_MPI\_CC}, {\tt I\_MPI\_CXX}, or {\tt I\_MPI\_F90} environment variables. This is an IntelMPI feature.
+
+The recommendation for Cray systems that use the Cray compiler wrappers {\tt cc}, {\tt CC}, and {\tt ftn},
+respectively, is to use {\tt ESMF\_OS=Unicos}. In most cases this setting is detected automatically by the ESMF
+build system, and should {\em not} be overridden.
+
+Under {\tt ESMF\_OS=Unicos}, with {\tt ESMF\_COMPILER=intel}, the C, C++, and Fortran compiler front-ends default to
+{\tt cc}, {\tt CC}, and {\tt ftn}, respectively, regardless of the  {\tt ESMF\_COMM} setting. The appropriate
+classic, oneAPI, or mixed compiler combination is typically determined by the Intel environment module loaded.
+Common module names on Cray systems are {\tt intel-classic}, {\tt intel-oneAPI}, and {\tt intel}, respectively.
+
+{\bf Tip: } Use the ESMF "{\tt make info}" target to query compiler version information. This can be used to determine the
+appropriate settings, and to diagnose issues before kicking off the complete ESMF build procedure.
+
 \subsection{Building the ESMF Library}
 \label{BuildESMF}