[analyzer] SATestBuild.py: fix broken string concatenation

This has been broken for a while, but the branch was never being taken.
(We were trying to do 'str + floatVal'; now we do 'str % intVal' and use
the '%d' format.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168174 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed