stdlib: Add method invocation without libffi
stdlib: Add method invocation without libffi

You can now add --define=NO_LIBFFI to the compile commandline, and you
get the ability to do runtime dynamic method invocation without
needing libffi.  This has the following caveats:
* The code is not very efficient
* It only supports up to six integer/pointer arguments and up to eight
  floating point arguments
* It only supports the System V ABI for AMD64 (this includes x86-64
  Linux and macOS, but *not* Windows)
* It's not incredibly well tested (though it seems to work on Linux
  with both clang and g++)

Plasmaworks/Rogue,Plasmaworks/Rogue,Plasmaworks/Rogue,Plasmaworks/Rogue,AbePralle/Rogue,AbePralle/Rogue