Debug info: Factor out the creation of DWARF expressions from AsmPrinter

into a new class DwarfExpression that can be shared between AsmPrinter
and DwarfUnit.

This is the first step towards unifying the two entirely redundant
implementations of dwarf expression emission in DwarfUnit and AsmPrinter.

Almost no functional change — Testcases were updated because asm comments
that used to be on two lines now appear on the same line, which is
actually preferable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225706 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/CMakeLists.txt

@@ -11,6 +11,7 @@ add_llvm_library(LLVMAsmPrinter
   DwarfCFIException.cpp
   DwarfCompileUnit.cpp
   DwarfDebug.cpp
+  DwarfExpression.cpp
   DwarfFile.cpp
   DwarfStringPool.cpp
   DwarfUnit.cpp