Test unit_tests failing in 32-bit release build.

After fixing #3450 , I've noticed that test unit_tests is failing:

[..]
1: testing asm call_switch_stack
1: EXPECT failed at /home/hgreving/dynamorio/src/core/arch/x86_code_test.c:61 in test check_var: *var
1/1 Test #1: unit_tests .......................***Failed 0.28 sec

0% tests passed, 1 tests failed out of 1

Total Test time (real) = 2.03 sec

The following tests FAILED:
1 - unit_tests (Failed)
Errors while running CTest