Add an easy way of disabling ASAN in cmake

Created by: Zaharid

ASAN is very useful for quickly finding errors but has several disadvantages:

• Difficult to make it work with Python (have to set an environment variable and maybe change some options to stop it from reporting garbage).
• Significantly slows down the code: By a factor of two or so.
• Virtual memory requirements can conflict with cluster limits.
• Incompatible with valgrind.

So it would be nice to be able to have a debug configuration but without ASAN readily available.