[libc] fix more -Wmissing-brace (#77382)

Similar to #77345, the buildbots are observing similar warnings for the sse2 implementation. llvm-project/libc/src/__support/HashTable/sse2/bitmask_impl.inc:36:13: error: suggest braces around initialization of subobject [-Werror,-Wmissing-braces] return {bitmask}; ^~~~~~~ { } llvm-project/libc/src/__support/HashTable/sse2/bitmask_impl.inc:45:13: error: suggest braces around initialization of subobject [-Werror,-Wmissing-braces] return {static_cast<uint16_t>(~mask_available().word)}; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ { } Link: https://lab.llvm.org/buildbot/#/builders/163/builds/49350/steps/8/logs/stdio Link: #74506

Author: nickdesaulniers

libc/src/__support/HashTable/sse2/bitmask_impl.inc

@@ -33,7 +33,7 @@ struct Group {
  LIBC_INLINE IteratableBitMask match_byte(uint8_t byte) const {
  auto cmp = _mm_cmpeq_epi8(data, _mm_set1_epi8(byte));
  auto bitmask = static_cast<uint16_t>(_mm_movemask_epi8(cmp));
- return {bitmask};
+ return {{bitmask}};
  }
 
  LIBC_INLINE BitMask mask_available() const {
@@ -42,7 +42,7 @@ struct Group {
  }
 
  LIBC_INLINE IteratableBitMask occupied() const {
- return {static_cast<uint16_t>(~mask_available().word)};
+ return {{static_cast<uint16_t>(~mask_available().word)}};
  }
 };
 } // namespace internal