cmake: find HDF4 under /usr/local/hdf4 and MacPorts, accept libhdf naming

HDF4 built with its own CMake build system (rather than autotools) is
commonly installed under a non-standard prefix like /usr/local/hdf4,
which CMake's default find_path/find_library search does not cover,
and names the low-level library 'hdf' instead of 'df'.

Verified working on macOS 27.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CMakeLists.txt

@@ -315,18 +315,26 @@ if (nexus)
   find_package(HDF5 COMPONENTS CXX REQUIRED)
   if (HAVE_HDF4)
     #--- check for HDF4 -----------------------------------------------------------
-    # Find HDF4 manually (pkg-config often doesn't have hdf4)
+    # Find HDF4 manually (pkg-config often doesn't have hdf4). In addition to the
+    # standard system locations, also look under /usr/local/hdf4 and /opt/local
+    # (MacPorts), which are common self-built/ported install prefixes and are not
+    # part of CMake's default search path. HDF4 built with its own CMake build
+    # system (as opposed to the autotools build) names the low-level library
+    # 'hdf' instead of 'df', so both names are accepted.
     find_path(HDF4_INCLUDE_DIR
       NAMES mfhdf.h
+      HINTS /usr/local/hdf4/include /opt/local/include/hdf
       PATH_SUFFIXES hdf
     )
 
     find_library(HDF4_DF_LIBRARY
-      NAMES df libdf
+      NAMES df libdf hdf libhdf
+      HINTS /usr/local/hdf4/lib /opt/local/lib
     )
 
     find_library(HDF4_MFHDF_LIBRARY
       NAMES mfhdf libmfhdf
+      HINTS /usr/local/hdf4/lib /opt/local/lib
     )
 
     if (HDF4_INCLUDE_DIR AND HDF4_DF_LIBRARY AND HDF4_MFHDF_LIBRARY)