[Debug Info] add DISubroutineType and its creation takes DITypeArray. 

DITypeArray is an array of DITypeRef, at its creation, we will create
DITypeRef (i.e use the identifier if the type node has an identifier).

This is the last patch to unique the type array of a subroutine type.

rdar://17628609


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214132 91177308-0d34-0410-b5e6-96231b3b80d8