Revert r149363 which was part a series of commits that were reverted in llvm

commit 149470. This fixes test/CodeGen/PR3589-freestanding-libcalls.c.

Original log:

    ConstantArray::get() (for strings) is going away, use
    ConstantDataArray::getString instead.

    Many instances of ConstantArray::get() could be moved to
    use more efficient ConstantDataArray methods that avoid a ton
    of intermediate Constant*'s for each element (e.g.
    GetConstantArrayFromStringLiteral).  I don't plan on doing this
    in the short-term though.

llvm-svn: 149477