Merge r101067 from mainline.
fix PR6660/6168: emit padding as zeros instead of undef.  Because 
trailing fields may not be represented in initializer lists, they
are being handled as padding and those fields *must* be zero 
initialized.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_27@101134 91177308-0d34-0410-b5e6-96231b3b80d8