Add flags to enable ASAN and UBSAN in build process

This is a change that was missing from the tree merged in with !83 (merged). It is obviously a very important piece as it allows for enabling the sanitizers in the first place. I assume it was removed by a rebase accidentally as it was the first commit.

Commit Description

You can now specify sanitize=yes to the make command, which enables the address and UB sanitizers. For Clang builds, it enables checks for unsigned integer ovewrflow and implicit conversions, additionally. Thus, it is advised to compile as follows:

make TOOLCHAIN=clang sanitize=yes

There also is the option to pass sanitize-strict=yes, which will set -fno-sanitize-recover= such that the program execution aborts in case the sanitizers detect something.