Add a DIELoc class to cover the DW_FORM_exprloc set of expressions

alongside DIEBlock and replace uses accordingly. Use DW_FORM_exprloc
in DWARF4 and later code. Update testcases.

Adding a DIELoc instead of using extra forms inside DIEBlock so
that we can keep location expressions separate from other uses. No
direct use at the moment, however, it's not a lot of code and
using a separately named class keeps it somewhat more obvious
what's going on in various locations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201481 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -43,7 +43,7 @@ class MCAsmInfo;
 class MCObjectFileInfo;
 class DIEAbbrev;
 class DIE;
-class DIEBlock;
+class DIELoc;
 class DIEEntry;
 
 //===----------------------------------------------------------------------===//