Tests, docs: Use sanitizer options from environment too.

Don't overwrite environment variables that may
contain options like suppression files, symboliser etc.
It's similar to rBa181b156399a13fa429159112e30c8005d5e8a59
and rBA589d13408a60cbec34a8bc3cc798c586043743ae .
For Blender Add-ons repo, see the equivalent in D9816.

Reviewed By: Blendify
Differential Revision: https://developer.blender.org/D9815

doc/python_api/sphinx_doc_gen.sh

@@ -55,7 +55,7 @@ if $DO_EXE_BLENDER ; then
   # Don't delete existing docs, now partial updates are used for quick builds.
   #
   # Disable ASAN error halt since it results in nonzero exit code on any minor issue.
-  ASAN_OPTIONS=halt_on_error=0 \
+  ASAN_OPTIONS=halt_on_error=0:${ASAN_OPTIONS} \
   $BLENDER_BIN \
     --background \
     -noaudio \