When initializing `revng::InitRevng` it is assumed by its parent,
`InitLLVM`, that the lifetime of `Argv` and be equivalent to
static, because it might be later retrieved to print it in case of a
crash. This works with the traditional `main`, however in the pipebox
the string passed are not guaranteed to have that lifetime. This commits
moves ownership of the strings to a class that stores them to avoid this
problem.
In the constructor of `InitRevng` also call all the `llvm::initialize*`
functions. This is done to be less implementation-specific and having
these functions be called in
`LLVMPipelineRegistry.libraryInitialization`.
This commit fixes command line parsing of revng through the
REVNG_OPTIONS environment variable. Previously the env was prepended to
the actual command-line variables, now it's appended, allowing to
specify command line arguments that depend on `-load`s.
Alessandro Di Federico