[testsuite,avr,trunk+4.7,committed]: Add LTO tests

[Georg-Johann Lay]

http://gcc.gnu.org/viewcvs?view=revision&revision=185793
http://gcc.gnu.org/viewcvs?view=revision&revision=185794

This adds LTO tests to avr-torture.exp:

        * gcc.target/avr/torture/avr-torture.exp (AVR_TORTURE_OPTIONS):
        Add "-Os -flto" to list.

Johann