Reduce the header declarations (#1342)

- Since we have style rules to include foo.hpp at the top of its
  corresponding foo.cpp, this takes any headers included by foo.hpp
  as being also guaranteed for foo.cpp.

- Use C-style <foo.h> instead of <cfoo>, since the latter only
  guarantees putting symbols in the `std` namespace, which we are
  not using for C functions (e.g. `printf` not `std::printf`).

- Remove now-unused `__PRETTY_FUNCTION__` reporting

include/itertools.hpp

@@ -6,13 +6,6 @@
 #include <tuple>
 #include <utility>
 
-#include "platform.hpp" // __PRETTY_FUNCTION__
-
-template<typename... Ts>
-static inline void report() {
-	puts(__PRETTY_FUNCTION__);
-}
-
 template<typename T>
 class EnumSeqIterator {
 	T _value;