Qt compilation crashes in different points of compilation, with the same state of make.conf configuration.
You might want to take a look at bug #20600.
*** Bug 36182 has been marked as a duplicate of this bug. ***
This sounds very very much like flaky hardware to me. Good luck, in bug #20600 there are various tips on diagnosing and solving
*** This bug has been marked as a duplicate of 20600 ***