Merge branch 'staging/dycore-without-physics' into develop (PR #1281)

This merge modifies the Makefile logic in src/core_atmosphere so that PHYSICS is
not defined whenever MPAS_CAM_DYCORE is found in CPPFLAGS. This removes the need
for any changes to src/core_atmosphere/Makefile when building MPAS-A as a dycore
in CAM-SIMA.

As before, it is still possible to manually un-define PHYSICS for stand-alone
MPAS-A by commenting-out or removing the definition of PHYSICS.

* staging/dycore-without-physics:
  Disable physics for MPAS dycore-only build

Author: mgduda

src/core_atmosphere/Makefile

@@ -4,8 +4,11 @@
 # To build a dycore-only MPAS-Atmosphere model, comment-out or delete
 # the definition of PHYSICS, below
 #
-PHYSICS=-DDO_PHYSICS
-
+# If MPAS_CAM_DYCORE is found in CPPFLAGS, PHYSICS will become undefined automatically
+#
+ifeq ($(findstring MPAS_CAM_DYCORE,$(CPPFLAGS)),)
+    PHYSICS = -DDO_PHYSICS
+endif
 
 ifdef PHYSICS
     PHYSCORE = physcore