C++ warning and build fixes (#707)

* Committing clang-format changes

* C++ build and warning updates

* Fixes all warnings on C++ (with gcc 9.3)
* Updates CMake and Autotools C++ builds

* Undo warning clobber

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

CMakeLists.txt

@@ -1125,7 +1125,6 @@ if (EXISTS "${HDF5_SOURCE_DIR}/c++" AND IS_DIRECTORY "${HDF5_SOURCE_DIR}/c++")
       endif ()
     endif ()
 
-    include (${HDF_RESOURCES_EXT_DIR}/HDFUseCXX.cmake)
     include (${HDF_RESOURCES_DIR}/HDFCXXCompilerFlags.cmake)
 
     add_subdirectory (c++)