[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: https://llvm.org/svn/llvm-project/libcxx/trunk@258900 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed