concurrent-ruby-ext: fix build on Darwin 32-bit #649

Job	Run time
Test isolated (2.3)	3m 51s
Test isolated (ruby)	3m 44s
Test without C extension	3m 19s
Tests: Ruby 3.3 - ubuntu	3m 20s
Tests: Ruby truffleruby - ubuntu	4m 29s
Tests: Ruby 2.4 - ubuntu	3m 33s
Tests: Ruby 2.6 - ubuntu	3m 30s
Tests: Ruby 2.7 - ubuntu	3m 32s
Tests: Ruby 3.4 - ubuntu	3m 25s
Tests: Ruby 2.5 - ubuntu	3m 29s
Tests: Ruby 3.0 - ubuntu	3m 18s
Tests: Ruby 3.2 - ubuntu	3m 21s
Tests: Ruby 3.1 - ubuntu	3m 23s
Tests: Ruby 2.3 - ubuntu	3m 30s
Tests: Ruby jruby - ubuntu	5m 41s
Tests: Ruby ruby - windows	4m 43s
	1h 0m 8s

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