Move common header files into a 'support' directory; make 'testit' include -I to that directory; rename 'iterators.h' to 'iterator_test.h'; remove hard-coded paths to include files from more than 350 source files

llvm-svn: 171594
diff --git a/libcxx/test/input.output/file.streams/fstreams/filebuf.virtuals/underflow.pass.cpp b/libcxx/test/input.output/file.streams/fstreams/filebuf.virtuals/underflow.pass.cpp
index af6c651..e34bc84 100644
--- a/libcxx/test/input.output/file.streams/fstreams/filebuf.virtuals/underflow.pass.cpp
+++ b/libcxx/test/input.output/file.streams/fstreams/filebuf.virtuals/underflow.pass.cpp
@@ -16,7 +16,7 @@
 #include <fstream>
 #include <cassert>
 
-#include "../../../../platform_support.h" // locale name macros
+#include "platform_support.h" // locale name macros
 
 template <class CharT>
 struct test_buf