Disable -Wcast-function-type-mismatch

Code owners should fix this.
```
.../obj/bionic/tests/stdio_ext_test.o.d -o out/soong/.intermediates/bionic/tests/libBionicStandardTests/android_x86_silvermont_static_cov/obj/bionic/tests/stdio_ext_test.o bionic/tests/stdio_ext_test.cpp
...test.cpp:251:31: error: cast from 'void (*)(std::atomic<pid_t> *)' (aka 'void (*)(atomic<int> *)') to 'void *(*)(void *)' converts to incompatible function type [-Werror,-Wcast-function-type-mismatch]
  251 |                               reinterpret_cast<void* (*)(void*)>(LockingByCallerHelper), &pid));
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Bug: b/353528991
Change-Id: I9b34705e220dc62ffe913c5942cb5ee8e43dd20e
Test: m checkbuild
diff --git a/tests/stdio_ext_test.cpp b/tests/stdio_ext_test.cpp
index dce1a66..56483f5 100644
--- a/tests/stdio_ext_test.cpp
+++ b/tests/stdio_ext_test.cpp
@@ -241,6 +241,8 @@
   funlockfile(stdout);
 }
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wcast-function-type-mismatch"
 TEST(stdio_ext, __fsetlocking_BYCALLER) {
   // Check if users can use flockfile/funlockfile to protect stdio operations.
   int old_state = __fsetlocking(stdout, FSETLOCKING_BYCALLER);
@@ -255,3 +257,4 @@
   ASSERT_EQ(0, pthread_join(thread, nullptr));
   __fsetlocking(stdout, old_state);
 }
+#pragma clang diagnostic pop