In the default case, we don't need to use the stack, we can save r7 with
ip register (that what does eglibc).
This allow to fix vfork data corruption
(see 3884bfe9661955543ce203c60f9225bbdf33f6bb), because vfork now don't
use the stack.
Used the new gensyscalls.py script to update the ARM syscalls with the
BEGIN(x) and END(x) macros to give size information for the code of the
syscall. Useful for valgrind.
Change-Id: I8c481c8928401ac110fd19b087f7d67e4db39326
