Support for _Atomic

CPAchecker fails to parse code that includes stdatomic.h due to definitions such as the following:

typedef _Atomic _Bool atomic_bool;

The problem here is the _Atomic, which is a syntax error for our parser (CDT).

We could work around this by adding a macro definition to EclipseCdtWrapper.StubScannerInfo that replaces _Atomic with the empty string, but of course this would not capture the intended semantics of atomic types, and CPAchecker would treat them like regular types instead. So maybe it is better to not do this? We should check if newer versions of CDT support parsing _Atomic. Maybe we also need to change something in the way how we call CDT and declare support for a newer C language version.