Merge branch 'check-pnetcdf-exists' into hotfix-v8.2.1 (PR #1203)

This merge improves the detection of the locations of the netCDF and pNetCDF
libraries.

Prior to this merge, the top-level Makefile contained logic to check for the
existence of directories $(NETCDF)/lib and $(NETCDF)/lib64, and similarly for
$(PNETCDF)/lib and $(PNETCDF)/lib64. This logic didn't actually include checks
on the presence of libraries within those directories.

Since the presence of a lib64/ directory was checked after the check for a lib/
directory, if, say, the netCDF library were installed in lib/ and not in lib64/,
the result of the Makefile logic would be an incorrect netCDF path of
$(NETCDF)/lib64 if a lib64/ directory was also present.

With this merge, the Makefile logic checks for the existence of libnetcdf.* or
libpnetcdf.* files within the lib/ and lib64/ directories before selecting a
directory for the path to netCDF or PnetCDF.

* check-pnetcdf-exists:
  Check for the libnetcdf library existence similar to pnetcdf
  Check for libpnetcdf library existence rather than just directory

Makefile

@@ -737,10 +737,10 @@ else # Not using PIO, using SMIOL
 endif
 
 ifneq "$(NETCDF)" ""
-ifneq ($(wildcard $(NETCDF)/lib), )
+ifneq ($(wildcard $(NETCDF)/lib/libnetcdf.*), )
 	NETCDFLIBLOC = lib
 endif
-ifneq ($(wildcard $(NETCDF)/lib64), )
+ifneq ($(wildcard $(NETCDF)/lib64/libnetcdf.*), )
 	NETCDFLIBLOC = lib64
 endif
 	CPPINCLUDES += -I$(NETCDF)/include
@@ -761,10 +761,10 @@ endif
 
 
 ifneq "$(PNETCDF)" ""
-ifneq ($(wildcard $(PNETCDF)/lib), )
+ifneq ($(wildcard $(PNETCDF)/lib/libpnetcdf.*), )
 	PNETCDFLIBLOC = lib
 endif
-ifneq ($(wildcard $(PNETCDF)/lib64), )
+ifneq ($(wildcard $(PNETCDF)/lib64/libpnetcdf.*), )
 	PNETCDFLIBLOC = lib64
 endif
 	CPPINCLUDES += -I$(PNETCDF)/include