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/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 999231a..8a8904d 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -5632,10 +5632,11 @@
     if (Arg *A = Args.getLastArg(options::OPT_g_Group)) {
       WantDebug = !A->getOption().matches(options::OPT_g0);
       if (WantDebug) {
-        if ((DwarfVersion = DwarfVersionNum(A->getSpelling())) == 0)
-          DwarfVersion = getToolChain().GetDefaultDwarfVersion();
+        DwarfVersion = DwarfVersionNum(A->getSpelling());
       }
     }
+    if (DwarfVersion == 0)
+      DwarfVersion = getToolChain().GetDefaultDwarfVersion();
     RenderDebugEnablingArgs(Args, CmdArgs,
                             (WantDebug ? CodeGenOptions::LimitedDebugInfo
                                        : CodeGenOptions::NoDebugInfo),