KVM: selftests: explicitly disable PIE for tests

KVM selftests embed the guest "image" as a function in the test itself
and extract the guest code at runtime by manually parsing the elf
headers.  The parsing is very simple and doesn't supporting fancy things
like position independent executables.  Recent versions of gcc enable
pie by default, which results in triple fault shutdowns in the guest due
to the virtual address in the headers not matching up with the virtual
address retrieved from the function pointer.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>