linux compat: define macros for syscalls

There is a lot of boilerplate we need to write whenever we want a syscall to be
reachable through the syscall function. This patch reduces that by only having
the implementer to specify the name and its arguments.

We can probably do slightly better than this, but I believe this is simple enough
already.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
libc: add pthread_attr_getguardsize() for porting CRuby

Signed-off-by: KANATSU Minoru <icc.pot.tyew272@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
vfs: fix namei() and friends

Add 'const' to function prototype of namei() and friends
to allow passing of a C++ converted string using c_str() which
return a const char*

Signed-off-by: Jaspal Singh Dhillon <jaspal.iiith@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>