Clean up #includes

Remove unused headers, and avoid relying on transitive inclusions

`include-what-you-use` has been very useful for this!

include/platform.hpp

@@ -7,11 +7,11 @@
 
 // MSVC doesn't have str(n)casecmp, use a suitable replacement
 #ifdef _MSC_VER
-	#include <string.h>
+	#include <string.h> // IWYU pragma: export
 	#define strcasecmp  _stricmp
 	#define strncasecmp _strnicmp
 #else
-	#include <strings.h>
+	#include <strings.h> // IWYU pragma: export
 #endif
 
 // MSVC prefixes the names of S_* macros with underscores,
@@ -24,21 +24,21 @@
 
 // MSVC doesn't use POSIX types or defines for `read`
 #ifdef _MSC_VER
-	#include <io.h>
+	#include <io.h> // IWYU pragma: export
 	#define STDIN_FILENO  0
 	#define STDOUT_FILENO 1
 	#define STDERR_FILENO 2
 	#define ssize_t       int
 	#define SSIZE_MAX     INT_MAX
 #else
-	#include <fcntl.h>
-	#include <limits.h>
-	#include <unistd.h>
+	#include <fcntl.h> // IWYU pragma: export
+	#include <limits.h> // IWYU pragma: export
+	#include <unistd.h> // IWYU pragma: export
 #endif
 
 // MSVC uses a different name for O_RDWR, and needs an additional _O_BINARY flag
 #ifdef _MSC_VER
-	#include <fcntl.h>
+	#include <fcntl.h> // IWYU pragma: export
 	#define O_RDWR         _O_RDWR
 	#define S_ISREG(field) ((field) & (_S_IFREG))
 	#define O_BINARY       _O_BINARY
@@ -50,7 +50,7 @@
 
 // Windows has stdin and stdout open as text by default, which we may not want
 #if defined(_MSC_VER) || defined(__MINGW32__)
-	#include <io.h>
+	#include <io.h> // IWYU pragma: export
 	#define setmode(fd, mode) _setmode(fd, mode)
 #else
 	#define setmode(fd, mode) (0)