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

This is the last patch to unique the type array of a subroutine type.
This is the paired commit with llvm r214132.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214133 91177308-0d34-0410-b5e6-96231b3b80d8