Do not include FastMalloc.h in config.h.

Source/wtf/NullPtr.h

Index: Source/wtf/NullPtr.h
diff --git a/Source/wtf/NullPtr.h b/Source/wtf/NullPtr.h
index a40a1d89b0bf303ee9be60f03689f8c323dbf037..1aa558498346d66d4ecbaf04b6ec7ce119d9282d 100644
--- a/Source/wtf/NullPtr.h
+++ b/Source/wtf/NullPtr.h
@@ -33,8 +33,6 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #if COMPILER_SUPPORTS(CXX_NULLPTR) || defined(_LIBCPP_VERSION)
 
-#include <cstddef>
-
 // libstdc++ supports nullptr_t starting with gcc 4.6. STLport doesn't define it.
 #if (defined(__GLIBCXX__) && __GLIBCXX__ < 20110325) || defined(_STLPORT_VERSION)
 namespace std {
@@ -44,6 +42,8 @@ typedef decltype(nullptr) nullptr_t;
 
 #else
 
+#include "wtf/WTFExport.h"
+
 namespace std {
 class nullptr_t {
 public: