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/platform.hpp

@@ -22,15 +22,6 @@
 	#define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
 #endif
 
-// gcc has __PRETTY_FUNCTION__, MSVC has __FUNCSIG__, __func__ is standard
-#ifndef __PRETTY_FUNCTION__
-	#ifdef __FUNCSIG__
-		#define __PRETTY_FUNCTION__ __FUNCSIG__
-	#else
-		#define __PRETTY_FUNCTION__ __func__
-	#endif
-#endif
-
 // MSVC doesn't use POSIX types or defines for `read`
 #ifdef _MSC_VER
 	#include <io.h>