[Driver] Remove unused #include of llvm/Support/config.h

This is a follow-up to r279112 (which removed the need for the header)
and in the same spirit as r279035 (which attempted to un-break
out-of-tree builds).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@279348 91177308-0d34-0410-b5e6-96231b3b80d8

tools/driver/cc1_main.cpp

@@ -25,7 +25,6 @@
 #include "clang/Frontend/Utils.h"
 #include "clang/FrontendTool/Utils.h"
 #include "llvm/ADT/Statistic.h"
-#include "llvm/Config/config.h"
 #include "llvm/LinkAllPasses.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/OptTable.h"