Makefile: use O3 for ompi_gnu_linux

Author: rmcdermo

Build/makefile

@@ -343,7 +343,7 @@ ompi_intel_linux : setup $(obj_mpi)
 
 #*** GNU Compilers ***
 
-ompi_gnu_linux : FFLAGS = -m64 -O2 -std=f2018 -frecursive -ffpe-summary=none -fall-intrinsics $(GITINFOGNU) $(FFLAGSMKL_GNU_OPENMPI) $(GFORTRAN_OPTIONS) $(FFLAGS_HYPRE) $(FFLAGS_SUNDIALS)
+ompi_gnu_linux : FFLAGS = -m64 -O3 -std=f2018 -frecursive -ffpe-summary=none -fall-intrinsics $(GITINFOGNU) $(FFLAGSMKL_GNU_OPENMPI) $(GFORTRAN_OPTIONS) $(FFLAGS_HYPRE) $(FFLAGS_SUNDIALS)
 ompi_gnu_linux : LFLAGSMKL = $(LFLAGSMKL_GNU_OPENMPI) $(LFLAGS_HYPRE) $(LFLAGS_SUNDIALS)
 ompi_gnu_linux : FCOMPL = $(COMP_FC)
 ompi_gnu_linux : FOPENMPFLAGS = -fopenmp