This adds two builtin kinds, ir_bk_va_start and ir_bk_va_arg. va_arg Builtins
are lowered in the lower_builtins pass with a function provided by the backend,
whereby most architectures can use be_default_lower_va_args. va_start Builtins
are lowered in the backend.

Note: This commit breaks all backends except for IA32. SPARC and AMD64 are
implemented in later commits. The ARM backend previously miscompiled variadic
functions, and will now throw a proper error.

* No \n at end; panic() adds one
* No punctuation mark at end
* Lowercase first letter

Deduce the mode automatically from the given entity.

This removes the strange entity/type duality and we get rid of union symconst_symbol.

also removed some assert(0) used in verifiers to stop when compiling
with assertions (you better use your debugger to stop and keep the code
clean)

It has been empty for nearly all systems. People who used to put stuff
in config.h can still create a config.h on their own and inject
-include (gcc) or /FI (msvc) into their CPPFLAGS.

Just state the copyright and the project the files belong to. You can
then find the COPYING file for the whole project.

This makes it consistent with other firm analyse functions. Also removes
the unnecessary return value.

The opcode list was a member of irprog before which wasn't really
handled consistently. Also make sure opcodes are properly freed at
ir_finish().