apigen: handle unsigned return types
taint: safely skip multiple calls to enable taint
fix LLVM helper call morpher

The LLVM helper call morpher casts the arguments to a helper to match
the helper's parameter types.
Previously, it checked each argument, until it found one that matched,
and then stopped. Now, it checks each argument and skips any that are
already the same type.
syscalls: remove unused variables code
plugins: syscalls: return-point callbacks return a code, can invalidate block

Make callbacks called at return from a syscall return an error code.
This give us the option of forcing QEMU to retranslate the code, if eg. we've
turned on LLVM.
syscalls: fix autogenerated weak callback file

The guard needs to be after we've #included the config, so that we can
actually check what has been defined.
syscalls: fdtracker: taint data from private files
syscalls: lots of cleanups and warning removals
syscalls: fdtracker: implement readv and writev
syscalls: fdtracker: enable/disable switch for tainting data

Enabled by uncommenting a line in the plugin's Makefile.
Defaults to off.
syscalls: correct signed/unsigned types, and more cleanup
syscalls: Linux prototype parser understands signed/unsigned uint32 types