Set i386 default target CPU to be i686 (same as gcc)

Closes: #812803
Index: llvm-toolchain-3.9-3.9/clang/lib/Driver/Tools.cpp
===================================================================
--- llvm-toolchain-3.9-3.9.orig/clang/lib/Driver/Tools.cpp
+++ llvm-toolchain-3.9-3.9/clang/lib/Driver/Tools.cpp
@@ -1898,6 +1898,7 @@ static const char *getX86TargetCPU(const
   case llvm::Triple::Haiku:
     return "i586";
   case llvm::Triple::Bitrig:
+  case llvm::Triple::Linux:
     return "i686";
   default:
     // Fallback to p4.