LibCore: Wrap commented out debug messages in a preprocessor define

We can also remove an outdated FIXME as dbg() does now support unsigned
longs :^)

Libraries/LibCore/Gzip.cpp

@@ -31,6 +31,8 @@
 #include <limits.h>
 #include <stddef.h>
 
+//#define DEBUG_GZIP
+
 namespace Core {
 
 bool Gzip::is_compressed(const ByteBuffer& data)
@@ -119,12 +121,14 @@ Optional<ByteBuffer> Gzip::decompress(const ByteBuffer& data)
  auto destination = ByteBuffer::create_uninitialized(1024);
  while (true) {
  unsigned long destination_len = destination.size();
- // FIXME: dbg() cannot take ulong?
- // dbg() << "Gzip::decompress: Calling puff()\n"
- // << " destination_data = " << destination.data() << "\n"
- // << " destination_len = " << (int)destination_len << "\n"
- // << " source_data = " << source.data() << "\n"
- // << " source_len = " << (int)source_len;
+
+#ifdef DEBUG_GZIP
+ dbg() << "Gzip::decompress: Calling puff()\n"
+ << " destination_data = " << destination.data() << "\n"
+ << " destination_len = " << destination_len << "\n"
+ << " source_data = " << source.data() << "\n"
+ << " source_len = " << source_len;
+#endif
 
  auto puff_ret = puff(
  destination.data(), &destination_len,