adjust ifort floating point options (MITgcm#408)

* adjust ifort floating point options
 - remove unused flag "-mp"
 - replace by recommended flag "-fp-model"

Author: mjlosch

doc/tag-index

@@ -1,6 +1,7 @@
     Notes on tags used in MITgcmUV
     ==============================
 
+o tools/build_options/linux_ia64_ifort_ollie: adjust floating point options
 o pkg/ctrl:
  - fix two bugs related to writing and reading control variables and
    corresponding gradients:

tools/build_options/linux_ia64_ifort_ollie

@@ -59,12 +59,16 @@ if test "x$IEEE" = x ; then     #- with optimisation:
     NOOPTFILES='obcs_init_fixed.F'
 else
   if test "x$DEVEL" = x ; then  #- no optimisation + IEEE :
-    # "-mp" is for ieee "maintain precision"
-    FOPTIM='-O0 -noalign -xHost -ip -mp'
+    # "-fp-model [keyword]" is the recommended method of controlling precision
+    FOPTIM='-O0 -noalign -xHost -ip -fp-model consistent'
+# alternatives, see man pages for details
+#   FOPTIM='-O0 -noalign -xHost -ip -mp1'
+#   FOPTIM='-O0 -noalign -xHost -ip -fp-model precise'
+#   FOPTIM='-O0 -noalign -xHost -ip -mieee-fp'
   else                          #- development/check options:
 #    FFLAGS="$FFLAGS -warn all -warn nounused"
     FFLAGS="$FFLAGS -warn unused"
-    FOPTIM="-fpe0 -check all -ftrapuv"
+    FOPTIM="-fpe0 -check all -ftrapuv -fp-model precise"
     FOPTIM="$FOPTIM -O0 -noalign -g -traceback"
   fi
 fi