folly/io/async/IoUringZeroCopyBufferPool.cpp: suppress -Wmissing-desi…

…gnated-field-initializers for iouring-related code

Summary:
This avoids the following errors, among quite a few others:

  folly/io/async/IoUringZeroCopyBufferPool.cpp:139:3: error: missing field 'id' initializer [-Werror,-Wmissing-designated-field-initializers]
  folly/io/async/IoUringZeroCopyBufferPool.cpp:145:3: error: missing field 'rq_area_token' initializer [-Werror,-Wmissing-designated-field-initializers]
  folly/io/async/IoUringZeroCopyBufferPool.cpp:153:3: error: missing field 'flags' initializer [-Werror,-Wmissing-designated-field-initializers]

The alternative would have been to add several initializations involving names like `__resv` and `__resv2`:
```
  .offsets = {.head = 0, .tail = 0, .rqes = 0, .__resv2},
  .__resv = 0,
```

Reviewed By: dmm-fb

Differential Revision: D70029686

fbshipit-source-id: 9ecfa29fc98ced4f2b5c71581f84e4a497b1b39c

folly/io/async/IoUringZeroCopyBufferPool.cpp

@@ -128,6 +128,9 @@ void IoUringZeroCopyBufferPool::mapMemory() {
   rqRingArea_ = static_cast<char*>(bufArea_) + bufAreaSize_;
 }
 
+FOLLY_PUSH_WARNING
+FOLLY_GNU_DISABLE_WARNING("-Wmissing-designated-field-initializers")
+
 void IoUringZeroCopyBufferPool::initialRegister(
     uint32_t ifindex, uint16_t queueId) {
   mapMemory();
@@ -152,6 +155,8 @@ void IoUringZeroCopyBufferPool::initialRegister(
       .region_ptr = reinterpret_cast<uint64_t>(&regionReg),
   };
 
+  FOLLY_POP_WARNING
+
   auto ret = io_uring_register_ifq(ring_, &ifqReg);
   if (ret) {
     ::munmap(bufArea_, bufAreaSize_ + rqRingAreaSize_);