[PATCH] CodeGen: Emit globals with a constant initializer but no definition as available_externally.

[Benjamin Kramer]

    @_ZN1S1qE = available_externally constant %struct.Q { i32* @_ZGRN1S1qE }, align 8
    @_ZGRN1S1qE = private global i32 0, align 4

  That doesn't look good :|

http://llvm-reviews.chandlerc.com/D1982