Ports: Upgrade to FFmpeg 5.0 release; enable SDL and networking

Ports/ffmpeg/patches/ReadMe.md

@@ -0,0 +1,9 @@
+# Patches for FFmpeg on SerenityOS
+
+## `errno-is-not-valid-during-cpp.patch`
+
+FFmpeg performs a preprocessor-time test on errno values. This test does
+not work on SerenityOS because our errno values are described by an
+enum, and therefore are only available at compile time.
+
+The patch removes the preprocessor-time test.

Ports/ffmpeg/patches/errno-is-not-valid-during-cpp.patch

@@ -0,0 +1,13 @@
+diff --git a/libavutil/error.h b/libavutil/error.h
+index 0d3269a..a54d80d 100644
+--- a/libavutil/error.h
++++ b/libavutil/error.h
+@@ -37,7 +37,7 @@
+ 
+ 
+ /* error handling */
+-#if EDOM > 0
++#if 1
+ #define AVERROR(e) (-(e))   ///< Returns a negative error code from a POSIX error code, to return from library functions.
+ #define AVUNERROR(e) (-(e)) ///< Returns a POSIX error code from a library function error return value.
+ #else