Fix a few cppcheck findings

cpu/native/irq_cpu.c

cpu/native/native_cpu.c

cpu/native/syscalls.c

cpu/x86/x86_memory.c

cpu/x86/x86_pci.c

cpu/x86/x86_pic.c

tests/test_float/main.c

tests/test_net_if/main.c

tests/test_thread_cooperation/main.c

tests/test_vtimer_msg_diff/main.c

tests/unittests/embunit/embUnit/TestSuite.c