Enable single precision build for JCSDA-internal/MPAS-Model (MPAS-Dev#27)

Description
This PR accompanies JCSDA-internal/mpas-jedi#728.
It solves single precision build for MPAS-Model: issue MPAS-Dev#26

To build
source env-setup/gnu-openmpi-cheyenne.sh
set(MPAS_DOUBLE_PRECISION "OFF" CACHE STRING ....) in mpas-bundle/CMakeLists.txt
ecbuild (cmake); make

Modified files
M CMakeLists.txt
M Makefile
M cmake/PackageConfig.cmake.in

Author: metdyn

CMakeLists.txt

@@ -100,6 +100,9 @@ macro(mpas_fortran_target _tgt)
     set_target_properties(${_tgt} PROPERTIES Fortran_FORMAT FREE)
     target_compile_definitions(${_tgt} PRIVATE _MPI=1)
     target_compile_definitions(${_tgt} PRIVATE USE_PIO2=1)
+    if(NOT MPAS_DOUBLE_PRECISION)
+      target_compile_definitions(${_tgt} PRIVATE "-DSINGLE_PRECISION")
+    endif()
 
     # Enable OpenMP support
     if(MPAS_OPENMP)

cmake/PackageConfig.cmake.in

@@ -88,6 +88,8 @@ else()
 endif()
 if(@MPAS_DOUBLE_PRECISION@) #MPAS_DOUBLE_PRECISION
     set(@PROJECT_NAME@_DOUBLE_PRECISION_FOUND True)
+else()
+    set(@PROJECT_NAME@_DOUBLE_PRECISION_FOUND False)
 endif()
 set(MPAS_CORES @MPAS_CORES@)
 foreach(_core IN LISTS MPAS_CORES)

src/core_atmosphere/physics/physics_wrf/module_ra_cam_support.F

@@ -8,7 +8,7 @@ MODULE module_ra_cam_support
   implicit none
       integer, parameter :: r8 = 8
       real(r8), parameter:: inf = 1.e20 ! CAM sets this differently in infnan.F90
-      integer, parameter:: bigint = O'17777777777'           ! largest possible 32-bit integer 
+      integer, parameter:: bigint = int(O'17777777777')   ! largest possible 32-bit integer 
 
       integer :: ixcldliq 
       integer :: ixcldice