Processing (*nix): use traditional fork-exec on Android and OpenBSD

Fix https://github.com/termux/termux-packages/issues/25369

src/common/io/io.h

@@ -222,6 +222,8 @@ static inline bool ffSearchUserConfigFile(const FFlist* configDirs, const char*
     return false;
 }
 
+FFNativeFD ffGetNullFD(void);
+
 #ifdef _WIN32
 // Only O_RDONLY is supported
 HANDLE openat(HANDLE dfd, const char* fileName, bool directory);

src/common/io/io_unix.c

@@ -358,3 +358,12 @@ void ffListFilesRecursively(const char* path, bool pretty)
     ffStrbufEnsureEndsWithC(&folder, '/');
     listFilesRecursively(folder.length, &folder, 0, NULL, pretty);
 }
+
+FFNativeFD ffGetNullFD(void)
+{
+    static FFNativeFD hNullFile = -1;
+    if (hNullFile != -1)
+        return hNullFile;
+    hNullFile = open("/dev/null", O_WRONLY | O_CLOEXEC);
+    return hNullFile;
+}