[libc++] Add -Wno-sized-deallocation to avoid spurious GCC warnings

GCC tries to be nice and tell us that we probably want to also implement
sized deallocation functions when we override the normal ones. However,
we know what we're doing in the test suite and don't want to override
them.

Author: ldionne

libcxx/utils/libcxx/test/config.py

@@ -526,6 +526,11 @@ def configure_warnings(self):
         self.cxx.addWarningFlagIfSupported('-Wno-noexcept-type')
         self.cxx.addWarningFlagIfSupported('-Wno-aligned-allocation-unavailable')
         self.cxx.addWarningFlagIfSupported('-Wno-atomic-alignment')
+
+        # GCC warns about places where we might want to add sized allocation/deallocation
+        # functions, but we know better what we're doing/testing in the test suite.
+        self.cxx.addWarningFlagIfSupported('-Wno-sized-deallocation')
+
         # These warnings should be enabled in order to support the MSVC
         # team using the test suite; They enable the warnings below and
         # expect the test suite to be clean.