Fix multi-block spanning libcall sequence

[Florian Weimer]

* Eric Botcazou:

> As for "complex" test cases, they are not supposed to go in the testsuite.
> In my experience, virtually all Ada testcases can be reduced to at most 3 
> files (2 specs + 1 body).

For some wrong-code bugs, I needed two bodies which are compiled
separately.  Perhaps it would have been possible to introduce the
optimization barrier in a different manner, but this approach seemed
to be the most reliable.