fix: track vendored FFmpeg config.h

Unignore and commit FFmpeg config.h so fresh clones have the expected vendored header.

Made-with: Cursor

thirdparty/rexglue-sdk/thirdparty/FFmpeg/.gitignore

@@ -30,7 +30,8 @@
 /ffplay
 /ffprobe
 /config.asm
-/config.h
+# ReXGlue vendors a pre-generated FFmpeg config header for deterministic builds.
+!/config.h
 /coverage.info
 /avversion.h
 /lcov/

thirdparty/rexglue-sdk/thirdparty/FFmpeg/config.h

@@ -0,0 +1,29 @@
+#if defined(WIN32) || defined(_WIN32)
+#if defined(__aarch64__) || defined(_M_ARM64)
+#include "config_windows_aarch64.h"
+#else
+#include "config_windows_x86_64.h"
+#endif
+#elif defined(__APPLE__) && defined(__MACH__)
+#if defined(__aarch64__) || defined(__arm64__)
+#include "config_macos_aarch64.h"
+#else
+#include "config_macos_x86_64.h"
+#endif
+#elif defined(__gnu_linux__)
+#if defined(__aarch64__)
+#include "config_linux_aarch64.h"
+#else
+#include "config_linux_x86_64.h"
+#endif
+#elif defined(__ANDROID__)
+#if defined(__aarch64__)
+#include "config_android_aarch64.h"
+#elif defined(__amd64__) || defined(__x86_64__)
+#include "config_android_x86_64.h"
+#else
+#error "android arch unsupported"
+#endif
+#else
+#error "no config"
+#endif