[libcxx] Remove -Wpadded from buildit script.
[libcxx] Remove -Wpadded from buildit script.

Per discussion with Eric and Joerg, this commit removes -Wpadded to
silence the warning about the padding inserted at the tail of struct
_Rep_base.

rdar://problem/23932550


git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@258900 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx