s390x regtest: Fix memcheck tests for cu21 and cu42 with Clang

s390x regtest: Fix memcheck tests for cu21 and cu42 with Clang

When compiled with Clang, the s390x memcheck tests for cu21 and cu42 yield
different line number information for the inline assemblies.  Using gcc,
the inline assemblies do not receive updated line number information
because they are phrased as if they were data, not code.  See also the
discussion in https://sourceware.org/bugzilla/show_bug.cgi?id=30206

Fix this by rephrasing the inline assemblies in cu21 and cu42 to normal
instructions, using the respective mnemonics.  Since this affects the line
number information, adjust the expected test output files as well.