user_only: compile everything with -fpie

user_only: compile everything with -fpie

We really need compile _all_ sources for user target with -fpie when
use --enable-user-pie.

It's regression introduced by commit add16157d72454.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
[blauwirbel@gmail.com: combined 299060a0 and 58faa1a6 to avoid breakage]
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>