Merge bitcoin#29529: fuzz: restrict fopencookie usage to Linux & FreeBSD

312f338 fuzz: restrict fopencookie usage to Linux & FreeBSD (fanquake)

Pull request description:

  Should fix the GCC compilation portion of bitcoin#29517 (comment).

  See also: https://www.gnu.org/software/gnulib/manual/html_node/fopencookie.html.

ACKs for top commit:
  m3dwards:
    ACK bitcoin@312f338
  TheCharlatan:
    utACK 312f338

Tree-SHA512: aa8ff20c3fa735415d05a93b8855877035c300f4d2dfd82f65fd9ed5b5c96ab619b4d84eef114ed0013dc5ff0800cb628ed3801e1efde0cfb0d426930d1673d5

src/test/fuzz/util.cpp

@@ -272,7 +272,7 @@ FILE* FuzzedFileProvider::open()
         [&] {
             mode = "a+";
         });
-#if defined _GNU_SOURCE && !defined __ANDROID__
+#if defined _GNU_SOURCE && (defined(__linux__) || defined(__FreeBSD__))
     const cookie_io_functions_t io_hooks = {
         FuzzedFileProvider::read,
         FuzzedFileProvider::write,