src: ignore GCC -Wcast-function-type for v8.h

Currently, the following warnings are emitted during compilation:
In file included from ../src/string_bytes.h:29,
                 from ../src/string_bytes.cc:22:
../deps/v8/include/v8.h:
In instantiation of ‘void v8::PersistentBase<T>::SetWeak(
    P*,typename v8::WeakCallbackInfo<P>::Callback, v8::WeakCallbackType)
[with P = node::BaseObject;
T = v8::Object;
typename v8::WeakCallbackInfo<P>::Callback =
    void (*)(const v8::WeakCallbackInfo<node::BaseObject>&)]’:
../src/base_object-inl.h:135:42:   required from here
../deps/v8/include/v8.h:10732:16: warning:
cast between incompatible function types from
‘v8::WeakCallbackInfo<node::BaseObject>::Callback’ {aka
‘void (*)(const v8::WeakCallbackInfo<node::BaseObject>&)’} to
‘Callback’ {aka ‘void (*)(const v8::WeakCallbackInfo<void>&)’}
[-Wcast-function-type]
10732 |                reinterpret_cast<Callback>(callback), type);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

And the same from test/cctest/test_aliased_buffer.cc

We have an open pull request against v8 for this:
https://chromium-review.googlesource.com/c/v8/v8/+/2080361

PR-URL: nodejs#32679
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/string_bytes.h

@@ -26,7 +26,14 @@
 
 // Decodes a v8::Local<v8::String> or Buffer to a raw char*
 
+#if (__GNUC__ >= 8) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wcast-function-type"
+#endif
 #include "v8.h"
+#if (__GNUC__ >= 8) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 #include "env-inl.h"
 
 #include <string>

test/cctest/test_aliased_buffer.cc

@@ -1,4 +1,11 @@
+#if (__GNUC__ >= 8) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wcast-function-type"
+#endif
 #include "v8.h"
+#if (__GNUC__ >= 8) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 #include "aliased_buffer.h"
 #include "node_test_fixture.h"