include clang's config.h unconditionally (v2)

And remove HAVE_CLANG_CONFIG_H, now that the header is generated
in the autoconf build, too.

Reverts r149571/restores r149504, now that config.h is generated
correctly by LLVM's configure in all build configurations.

llvm-svn: 150487
diff --git a/clang/lib/Frontend/InitHeaderSearch.cpp b/clang/lib/Frontend/InitHeaderSearch.cpp
index 67b2287..ee4b4eb 100644
--- a/clang/lib/Frontend/InitHeaderSearch.cpp
+++ b/clang/lib/Frontend/InitHeaderSearch.cpp
@@ -26,11 +26,8 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Path.h"
 
-#ifdef HAVE_CLANG_CONFIG_H
-# include "clang/Config/config.h"
-#endif
+#include "clang/Config/config.h" // C_INCLUDE_DIRS
 
-#include "llvm/Config/config.h"
 using namespace clang;
 using namespace clang::frontend;