Support `.exe` file extension in `Makefile` on MSYS2 #3454

Job	Run time
check_format	1m 37s
x86_64-gnu-test (1.7.3)	4m 22s
x86_64-gnu-test-preview_mt	5m 44s
x86_64-gnu-test (1.8.2)	3m 16s
x86_64-gnu-test (1.9.2)	2m 58s
x86_64-musl-test	31m 35s
x86_64-gnu-test (1.10.1)	30m 2s
x86_64-gnu-test (1.11.2)	29m 57s
x86_64-gnu-test (1.12.2)	29m 49s
x86_64-gnu-test (1.13.3)	25m 56s
x86_64-gnu-test (1.14.0)	22m 6s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	31m 7s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	30m 54s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	22m 4s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	14m 43s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	14m 7s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	6m 4s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	4m 22s
	5h 10m 43s

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