[patch/idea] Add register scrambling to testsuite

[DJ Delorie]

Noah Goldstein <goldstein.w.n@gmail.com> writes:
>> +  asm volatile ("mov %0, %%r11" :: "i" (0x12345679));  \
> Do these statements need to specify the register they are clobbering?

Er, yes.  Despite being in an isolated function and volatile, I keep
forgetting that LTO invalidates those considerations.

I'm also hoping that the platform maintainers will step up and provide
the appropriate clobber lists anyway ;-)