Merge 82194 from mainline.
don't stick an uninitialized 'stat' buf into the stat cache, fill it
with zeros.  This avoids a GCC warning (PR5000)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_26@82195 91177308-0d34-0410-b5e6-96231b3b80d8