lib/fuzzing: Support an oss-fuzz build with either address or undefined behaviour...

lib/fuzzing: Support an oss-fuzz build with either address or undefined behaviour sanitizers

Add handler for $SANITIZER in build.sh

This allows a build with the undefined behaviour sanitizer.

Otherwise we fail the oss-fuzz CI because the UBSan build links with ASan.

Once this in in then https://github.com/google/oss-fuzz/pull/3094
can be merged to oss-fuzz.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>