Set PWD in Makefile

When cross-compiling using e.g. buildroot, PWD was not reset in the Makefile.
That caused PWD to have an incorrect value, and thus building the module failed.

Signed-off-by: Anders Darander <anders@chargestorm.se>
interpreter/vm.c: include uaccess.h

otherwise functions, such as copy_from_user, is implicitly defined.

Signed-off-by: Anders Darander <anders@chargestorm.se>