Add debug and valgrind to LLVM tests and config

[marvinborner]

This makes use of the --debug flag and adds a new flag --valgrind:

• --debug: Use GCC's sanitization and other debugging flags (LLVM only for now)
• --valgrind: Run the final executable using valgrind and disable optimizations during compilation. This is enabled by default for LLVM tests.

This will make a lot of LLVM tests fail (intended).

[b-studios]

Sadly this means I cannot run tests anymore :(