Resolves#15921
The test case nptl/tst-cleanup2 fails on s390x and power6 due to
instruction sheduling in gcc. This was reported in gcc:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58034
but it was concluded that gcc is allowed to assume that the first
argument to sprintf is a character array - NULL not being a valid
character array.