Write out the plane for types first, since values of primitive types

Write out the plane for types first, since values of primitive types
may be constructed by expressions of other types (and so the
contents of the primitive type planes must come after all types).
Use a helper function outputConstantsInPlane in outputConstants to
do this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2898 91177308-0d34-0410-b5e6-96231b3b80d8