Size optimization for syscalls

[ExtendeD]

_SYSCALL_GETSAVEDLR_PTR() is quite heavy and could be shared as a function (actually two, for arm an thumb).

This requires nspire-ld to link the programs with an internal static library (ndlslib?).

Syscalls with var args or with more than 4 parameters currently produce static functions (i.e. potential duplicates). They could also be shared as non-static functions.

os.h can still offer macros for automatic generation of these functions.