Libc (macOS): detect libSystem version

src/detection/libc/libc_apple.c

@@ -0,0 +1,13 @@
+#include "libc.h"
+
+const char* ffDetectLibc(FFLibcResult* result)
+{
+    result->name = "libSystem";
+
+#ifdef FF_LIBSYSTEM_VERSION
+    result->version = FF_LIBSYSTEM_VERSION;
+#else
+    result->version = NULL;
+#endif
+    return NULL;
+}