asm/unistd.h includes asm/unistd_64.h on x86_64
and asm/unistd_32.h on i386 but these files are
generated files in 3.4 and when we do 'make clean' they get
deleted and it shows up as an error when building
external modules. May be its a 3.4 kernel bug may be not
but make clean should have left the tree in
a shape to build modules but it does not.
Probably we should run make modules_prepare after having
run make clean.
