libstdc++: replace bit_set::operator!= in ityp_bitset

C++20 removed the operator.

Bug: chromium:957519
Change-Id: Iba9c3fcdf4d7d3c4286b5f5dac86304faa6a0c02
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/104201
Commit-Queue: Stephan Hartmann <stha09@googlemail.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/dawn/common/ityp_bitset.h

@@ -58,7 +58,7 @@ class bitset : private std::bitset<N> {
     }
 
     bool operator!=(const bitset& other) const noexcept {
-        return Base::operator!=(static_cast<const Base&>(other));
+        return !Base::operator==(static_cast<const Base&>(other));
     }
 
     bitset& operator&=(const bitset& other) noexcept {