FindHDF5: Restore pre-3.6 behavior of finding only C by default

Refactoring in commit v3.6.0-rc1~72^2 (HDF5: Rework component searching
to correctly find HL for all bindings, 2016-05-12) changed the default
behavior from finding only the C bindings to finding everything for the
enabled languages.  Restore the original behavior for compatibility and
because many projects need only the C bindings.

Closes: #16397

Modules/FindHDF5.cmake

@@ -111,18 +111,10 @@ include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
 set(HDF5_VALID_LANGUAGE_BINDINGS C CXX Fortran)
 
 # Validate the list of find components.
-set(HDF5_LANGUAGE_BINDINGS)
 if(NOT HDF5_FIND_COMPONENTS)
-  get_property(__langs GLOBAL PROPERTY ENABLED_LANGUAGES)
-  foreach(__lang IN LISTS __langs)
-    if(__lang MATCHES "^(C|CXX|Fortran)$")
-      list(APPEND HDF5_LANGUAGE_BINDINGS ${__lang})
-      set(HDF5_FIND_REQUIRED_${__lang} True)
-    endif()
-  endforeach()
-  set(FIND_HL ON)
-  set(HDF5_FIND_REQUIRED_HL True)
+  set(HDF5_LANGUAGE_BINDINGS "C")
 else()
+  set(HDF5_LANGUAGE_BINDINGS)
   # add the extra specified components, ensuring that they are valid.
   set(FIND_HL OFF)
   foreach(component IN LISTS HDF5_FIND_COMPONENTS)