Unit Tests failing when built with clang 12

[Stephan Bergmann]

On 16/03/2021 23:05, slacka wrote:
> Yes, I just verified that you'll need an --enable-optimized build to
> reproduce this failure. When I built with clang 12 + --enable-debug, all
> unit tests passed.

though a Clang 13 trunk build with --enable-optimized (and 
--disable-debug, --disable-dbgutil) runs UITest_calc_tests9 successfully 
for me