Need additional include flags for GNU compiler

[climbfuji]

For some users and/or on some systems, the recent dycore update requires adding an additional include flag in the top-level makefile:

dom.heinzeller@heinzeller-lt:~/scratch/ufs-weather-model/ufs-weather-model-jun-tomsfix-20200626/FV3/atmos_cubed_sphere [gnupy3dev]> git diff
diff --git a/makefile b/makefile
index 530a73d..e35a9ba 100644
--- a/makefile
+++ b/makefile
@@ -23,7 +23,7 @@ endif

 LIBRARY  = libfv3core.a

-FFLAGS   += -I$(FMS_DIR) -I../gfsphysics -I../ipd -I../io
+FFLAGS   += -I$(FMS_DIR) -I../gfsphysics -I../ipd -I../io -I.

 SRCS_f   =

Without these, users may get an error message

tools/fv_eta.F90:291:2:

  291 |
      |  1
Fatal Error: tools/fv_eta.h: No such file or directory
compilation terminated.
../conf/make.rules:20: recipe for target 'tools/fv_eta.o' failed
gmake[2]: *** [tools/fv_eta.o] Error 1

[climbfuji]

This was fixed in the NCAR dtc/develop branch in PR NCAR#14, commit cbbf2e8. This can be cherry-picked and committed to dev/emc if needed.