Corrects lib lookup in case-sensitive OSes (#15362) #13270

Job	Run time
check_format	1m 34s
x86_64-gnu-test (1.7.3)	35m 20s
x86_64-gnu-test (1.8.2)	36m 2s
x86_64-gnu-test (1.9.2)	32m 30s
x86_64-gnu-test (1.10.1)	32m 41s
x86_64-gnu-test (1.11.2)	32m 49s
x86_64-gnu-test (1.12.2)	33m 34s
x86_64-gnu-test (1.13.3)	33m 37s
x86_64-gnu-test-preview_mt	5m 50s
x86_64-gnu-test (1.14.1)	34m 44s
x86_64-gnu-test (1.15.0)	38m 18s
x86_64-musl-test	38m 28s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 46s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 50s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	36m 25s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	34m 3s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	34m 50s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	34m 51s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	35m 41s
	9h 58m 53s

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