Always pass a -dwarf-version argument to integrated as.

This removes the default of 3 hidden in the assembler previously.

Fixes breakage caused by r249655, reported by vsukharev.

llvm-svn: 250173
diff --git a/clang/tools/driver/cc1as_main.cpp b/clang/tools/driver/cc1as_main.cpp
index 54a77ed..d98ba6e 100644
--- a/clang/tools/driver/cc1as_main.cpp
+++ b/clang/tools/driver/cc1as_main.cpp
@@ -144,7 +144,7 @@
     RelaxAll = 0;
     NoExecStack = 0;
     FatalWarnings = 0;
-    DwarfVersion = 3;
+    DwarfVersion = 0;
   }
 
   static bool CreateFromArgs(AssemblerInvocation &Res,