malloc elimination: it's a bad idea to use raw_svector_ostream on a

malloc elimination: it's a bad idea to use raw_svector_ostream on a
small heap-allocated SmallString because it unconditionally forces a malloc.

(Revised version of r129688, with the necessary flush() call.)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129716 91177308-0d34-0410-b5e6-96231b3b80d8