openvdb: Import some upstream patches. Fix python module extension.

Still missing some symbols in DLL that prevent build blender with
openvdb

mingw-w64-openvdb/004-python-module-ext.patch

@@ -0,0 +1,13 @@
+--- a/openvdb/python/CMakeLists.txt
++++ b/openvdb/python/CMakeLists.txt
+@@ -271,7 +271,9 @@
+ if(UNIX)
+   set_target_properties(pyopenvdb PROPERTIES SUFFIX ".so") # must be .so (not .dylib)
+ elseif(WIN32)
+-  set_target_properties(pyopenvdb PROPERTIES SUFFIX ".pyd") # .pyd on windows
++  execute_process(COMMAND ${PYTHON_EXECUTABLE} -c "import distutils.sysconfig, sys; get = distutils.sysconfig.get_config_var; sys.stdout.write(get('EXT_SUFFIX') or get('SO') or '.pyd');"
++                  OUTPUT_VARIABLE PYTHON_MOD_EXT)
++  set_target_properties(pyopenvdb PROPERTIES SUFFIX "${PYTHON_MOD_EXT}")
+ endif()
+ 
+ target_include_directories(pyopenvdb SYSTEM PUBLIC ${OPENVDB_PYTHON_INCLUDES})