Protect constant initializers with mutex on Windows #3464

Job	Run time
check_format	1m 34s
x86_64-gnu-test (1.7.3)	34m 21s
x86_64-gnu-test-preview_mt	5m 44s
x86_64-musl-test	38m 52s
x86_64-gnu-test (1.8.2)	33m 9s
x86_64-gnu-test (1.9.2)	33m 17s
x86_64-gnu-test (1.10.1)	38m 7s
x86_64-gnu-test (1.11.2)	35m 21s
x86_64-gnu-test (1.12.2)	33m 51s
x86_64-gnu-test (1.13.3)	33m 51s
x86_64-gnu-test (1.14.0)	34m 25s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 4s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	43m 34s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	35m 12s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	32m 54s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	34m 40s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	34m 38s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	33m 30s
	9h 30m 4s

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