dep/msvc: Update SDL2 to 2.0.16

dep/msvc/sdl2/include/SDL_error.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2019 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -37,9 +37,88 @@ extern "C" {
 #endif
 
 /* Public functions */
-/* SDL_SetError() unconditionally returns -1. */
+
+
+/**
+ * Set the SDL error message for the current thread.
+ *
+ * Calling this function will replace any previous error message that was set.
+ *
+ * This function always returns -1, since SDL frequently uses -1 to signify an
+ * failing result, leading to this idiom:
+ *
+ * ```c
+ * if (error_code) {
+ *     return SDL_SetError("This operation has failed: %d", error_code);
+ * }
+ * ```
+ *
+ * \param fmt a printf()-style message format string
+ * \param ... additional parameters matching % tokens in the `fmt` string, if
+ *            any
+ * \returns always -1.
+ *
+ * \sa SDL_ClearError
+ * \sa SDL_GetError
+ */
 extern DECLSPEC int SDLCALL SDL_SetError(SDL_PRINTF_FORMAT_STRING const char *fmt, ...) SDL_PRINTF_VARARG_FUNC(1);
+
+/**
+ * Retrieve a message about the last error that occurred on the current
+ * thread.
+ *
+ * It is possible for multiple errors to occur before calling SDL_GetError().
+ * Only the last error is returned.
+ *
+ * The message is only applicable when an SDL function has signaled an error.
+ * You must check the return values of SDL function calls to determine when to
+ * appropriately call SDL_GetError(). You should _not_ use the results of
+ * SDL_GetError() to decide if an error has occurred! Sometimes SDL will set
+ * an error string even when reporting success.
+ *
+ * SDL will _not_ clear the error string for successful API calls. You _must_
+ * check return values for failure cases before you can assume the error
+ * string applies.
+ *
+ * Error strings are set per-thread, so an error set in a different thread
+ * will not interfere with the current thread's operation.
+ *
+ * The returned string is internally allocated and must not be freed by the
+ * application.
+ *
+ * \returns a message with information about the specific error that occurred,
+ *          or an empty string if there hasn't been an error message set since
+ *          the last call to SDL_ClearError(). The message is only applicable
+ *          when an SDL function has signaled an error. You must check the
+ *          return values of SDL function calls to determine when to
+ *          appropriately call SDL_GetError().
+ *
+ * \sa SDL_ClearError
+ * \sa SDL_SetError
+ */
 extern DECLSPEC const char *SDLCALL SDL_GetError(void);
+
+/**
+ * Get the last error message that was set for the current thread.
+ *
+ * This allows the caller to copy the error string into a provided buffer, but
+ * otherwise operates exactly the same as SDL_GetError().
+ *
+ * \param errstr A buffer to fill with the last error message that was set for
+ *               the current thread
+ * \param maxlen The size of the buffer pointed to by the errstr parameter
+ * \returns the pointer passed in as the `errstr` parameter.
+ *
+ * \sa SDL_GetError
+ */
+extern DECLSPEC char * SDLCALL SDL_GetErrorMsg(char *errstr, int maxlen);
+
+/**
+ * Clear any previous error message for this thread.
+ *
+ * \sa SDL_GetError
+ * \sa SDL_SetError
+ */
 extern DECLSPEC void SDLCALL SDL_ClearError(void);
 
 /**