CONFIG: update Fujitsu rules (#1671)

- openmp using the libfjomp

- fastmath as per the ArmClang compiler

wmake/rules/linuxARM64Fujitsu/c++Opt

 c++DBUG     =
-c++OPT      = -O3
+c++OPT      = -ffp-contract=fast -ffast-math -O3 -funsafe-math-optimizations

wmake/rules/linuxARM64Fujitsu/cOpt

 cDBUG       =
-cOPT        = -O3
+cOPT        = -ffp-contract=fast -ffast-math -O3

wmake/rules/linuxARM64Fujitsu/general

@@ -3,7 +3,16 @@ CPP        = cpp -traditional-cpp $(GFLAGS)
 PROJECT_LIBS = -l$(WM_PROJECT) -ldl
 
 include $(GENERAL_RULES)/standard
-include $(GENERAL_RULES)/Clang/openmp
+## include $(GENERAL_RULES)/Clang/openmp
+
+# Fujitsu-specific
+# ----
+COMP_OPENMP = -DUSE_OMP -fopenmp
+LINK_OPENMP = -lfjomp
+# ----
+# Or disable
+# include $(GENERAL_RULES)/no-openmp
+# ----
 
 include $(DEFAULT_RULES)/c
 include $(DEFAULT_RULES)/c++