Add variant openmp for package esmf (spack#2635)

Author: climbfuji

repos/spack_repo/builtin/packages/esmf/package.py

@@ -46,6 +46,7 @@ class Esmf(MakefilePackage, PythonExtension):
     version("8.0.1", sha256="13ce2ca0ae622548c00f7bb18317fb100235ca8b7ddbfac7e201a339e8eb05a3")
 
     variant("mpi", default=True, description="Build with MPI support")
+    variant("openmp", default=True, description="Build with OpenMP support")
     variant("external-lapack", default=False, description="Build with external LAPACK library")
     variant("netcdf", default=True, description="Build with NetCDF support")
     variant("pnetcdf", default=False, description="Build with pNetCDF support")
@@ -312,6 +313,15 @@ def setup_build_environment(self, env: EnvironmentModifications) -> None:
         if comm_variant != "auto":
             env.set("ESMF_COMM", comm_variant)
 
+        ##########
+        # OpenMP #
+        ##########
+
+        if spec.satisfies("+openmp"):
+            env.set("ESMF_OPENMP", "ON")
+        else:
+            env.set("ESMF_OPENMP", "OFF")
+
         ##########
         # LAPACK #
         ##########