runtime error with Izumi_nag -- doesn't like NaN's in _FillValue?

The following test fails at runtime with the NAG compiler on Izumi. It seems to dislike _FillValue being set to NaN.

SMS_D_Ld5.5x5_amazon_rHDMA.I2000Clm60SpMizGs.izumi_nag.mizuroute-default

cesm.log:
```
Attribute logunit not set for ROF
ROF: PIO numiotasks= 1
ROF: PIO stride= 24
ROF: PIO rearranger= 2
ROF: PIO root= 1
shr_file_mod.F90 913 This routine is depricated - use shr_log_setLogUnit instead -2134114300
ERROR: 0 NetCDF: Not a valid data type or _FillValue type mismatch err_num = -45 fname = /fs/cgd/data0/erik/ctsm_worktree/answer_changes/libraries/parallelio/src/clib/pioc_support.c line = 2457
[cli_0]: aborting job:
```

The mizuRoute gets to the middle of the initialization as follows.

rof.log:
```
---- mis. routing options ---
Lateral flow drains at the top of headwater reaches only for IRF, KWE, MC, DW
mizuRoute initialization
mizuRoute npes = 24
mizuRoute iam = 0
mizuRoute cal = noleap
mizuRoute time = days since 2000-01-01 00:00:00
inst_name = ROF
mizuRoute tracers= LIQ: ICE:
(route_ini) mizuRoute run at 86400.0000000 [sec] step 1 per a coupling
define run:
run type = initial
coupling_frequency = 8.6400000000000000E+04 [day]
mizuRoute timestep = 8.6400000000000000E+04 [sec]
```