build: use non-deprecated compiler flag when building jruby extension… #640

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 3.1	16s
ubuntu-24.04 truffleruby-head	45s
ubuntu-24.04 4.0	19s
ubuntu-24.04 3.4	21s
ubuntu-24.04 head	22s
ubuntu-24.04 3.2	16s
ubuntu-24.04 2.7	44s
ubuntu-24.04 debug	29s
ubuntu-22.04 3.1	19s
ubuntu-24.04 3.0	15s
ubuntu-24.04 3.3	16s
ubuntu-22.04 3.4	20s
ubuntu-22.04 2.7	48s
ubuntu-22.04 truffleruby-head	53s
ubuntu-24.04 jruby-head	1m 11s
ubuntu-22.04 3.3	21s
ubuntu-22.04 3.2	19s
ubuntu-22.04 4.0	22s
ubuntu-22.04 3.0	20s
ubuntu-22.04 head	25s
ubuntu-22.04 debug	29s
ubuntu-22.04 jruby-head	1m 17s
	11m 11s

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