SuiteSparsePolicy.cmake: document the change to SUITESPARSE_USE_FORTRAN

Author: DrTimothyAldenDavis

cmake_modules/SuiteSparsePolicy.cmake

@@ -72,6 +72,21 @@
 #                       for your system.
 #                       Default: OFF
 #
+#       This setting was ON by default in SuiteSparse 7.10.0 and earlier.
+#       Note that Fortran is now disabled by default, with the default setting
+#       of SUITESPARSE_USE_FORTRAN changed from ON to OFF.  If the icx compiler
+#       and the Intel MKL BLAS are available but ifx is not, then loading the
+#       GNU Fortran compiler causes the cmake FindBLAS to link the Intel MKL
+#       against libgomp, but at the same time cmake links the application with
+#       libiomp.  Including two OpenMP libraries, libiomp and libgomp, in one
+#       application can cause serious performance issues.  To avoid this issue,
+#       SUITESPARSE_USE_FORTRAN has been set to OFF.  This has little impact on
+#       SuiteSparse (it disables the AMD Fortran routines, and removes the
+#       Fortran interface to UMFPACK).  If you wish to use those features,
+#       re-enable the SUITESPARSE_USE_FORTRAN, but be sure to use either gcc
+#       and gfortran together, or icx and ifx together.  Do not mix-and-match
+#       the compilers.
+#
 #   SUITESPARSE_PKGFILEDIR: Directory where CMake Config and pkg-config files
 #                       will be installed.  By default, CMake Config files will
 #                       be installed in the subfolder `cmake` of the directory