Silence GCC warnings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@147664 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index e69e2cb..76be9bd 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -737,7 +737,7 @@
   const Driver &D = getToolChain().getDriver();
 
   StringRef ArchName;
-  const char *CPUName;
+  const char *CPUName = 0;
 
   // Set target cpu and architecture.
   if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {