avoid using config.h in public headers
This is the only usage in clang's headers, and it's for a define
that only exists on CMake builds for the sake of the MSVC compiler,
so just use an ifdef instead.
Also add an include for config.h in a file that actually needs it,
and was picking it up by accident indirectly.
llvm-svn: 133710
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 38fcfe3..cb91c89 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -38,6 +38,7 @@
#include "llvm/Support/Program.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/system_error.h"
+#include "llvm/Config/config.h"
using namespace clang;
CompilerInstance::CompilerInstance()