From: Caroline Tice <cmtice@google.com>

llvm-3.9-dwarf-version

This is a temporary workaround.

Currently LLVM generates Dwarf version 4 for all of its debug
information, including its Debug Frames (CIE) information. 
Breakpad cannot handle Dwarf Version 4 (see
https://bugs.chromium.org/p/chromium/issues/detail?id=614788).  We
tried reducing all of the Dwarf information to version 3, but that
causes problems with Fission (the splitting of debug information into
separate files), which requires the Dwarf DIEs to be emitted at
version 4.  This patch works around that issue by forcing the Debug
Frames version of Dwarf to be version 1, while leaving the rest of the
Dwarf data at version 4.  When the replacement for Breakpad comes out
we will no longer need this patch, as that is supposed to be able to
handle version 4 frames information.

index 759f90e..d536397 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -1252,7 +1252,8 @@ static unsigned getCIEVersion(bool IsEH, unsigned DwarfVersion) {
     return 3;
   case 4:
   case 5:
-    return 4;
+    return 1;
+    //    return 4;  Temporarily disable as workaround for Breakpad issue
   }
   llvm_unreachable("Unknown version");
 }