XCore target: remove incorrect DebugLoc entries from prologue

Summary: This was causing the prologue_end to be incorrectly positioned.

Differential Revision: http://reviews.llvm.org/D4122

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212318 91177308-0d34-0410-b5e6-96231b3b80d8